Rice Crop Timeline for the Southern States of Arkansas, Louisiana and Mississippi

Rice Crop Timeline for the Southern States of Arkansas, Louisiana and Mississippi
Rice Crop Timeline for the Southern States of
Arkansas, Louisiana, and Mississippi
Matt Shipp, Louisiana State University
INTRODUCTION
This timeline has been created to give a general overview of crop
production, worker activities, and key pests of rice grown in Arkansas, Louisiana,
and Mississippi. This document is intended to describe the activities and their
relationship to pesticide applications that take place in the field throughout the
crop cycle. Pesticide use recommendations are current as of 2002.
CROP PRODUCTION
Arkansas, Louisiana, and Mississippi rank 1, 2, and 4, respectively, for rice
production within the United States. The three states had a combined total of
2,420,000 acres harvested in 2001. The value of these acres was slightly over
$640,000,000 and represented 72% of the nation’s total.
Short grain – Arkansas
Medium grain – Arkansas and Louisiana
Long grain – Arkansas, Louisiana, and Mississippi
Rice thrives in the warmer temperate regions of the south. It can be
cultivated in almost any soil type other than deep sand. An important factor,
regardless of soil texture, is the presence of an impervious subsoil layer in the
form of a fragipan or clay horizon minimizing the percolation of water. The idea
is to be able to maintain water in the fields which are, in essence, shallow ponds.
LAND AND SEEDBED PREPARATION
Leveling and Drainage Considerations
Fields for growing rice should be relatively level but gently sloping toward
drainage ditches. Ideally, land leveling for a uniform grade of 0.2 percent slope
or less provides the following: (1) necessary early drainage in the spring for early
soil preparation which permits early seeding, (2) uniform flood depth which
reduces the amount of water needed for irrigation, and (3) the need for fewer
levees.
Importance of Early Land Preparation
Timely land preparation is essential for successful rice production.
Therefore, plow fields in the summer or early fall. Early land preparation is
particularly critical when high residue crops such as grain sorghum or corn are
planted the year before rice. If land has been out of production and is grown up
in weeds and brush, prepare the land as early as possible. Early land
preparation allows several stands of grass and red rice to be killed by surface
cultivation before planting.
Early land preparation incorporates the crop residue to insure good
decomposition of plant material which prevents early-season nitrogen deficiency.
If early land preparation is not possible, decomposition will not be at an advanced
stage at planting time. Since the soil’s microorganisms (bacteria, fungi, etc.) that
decompose crop residue are competing with rice plants for nutrients, particularly
nitrogen, the rice plant will show nitrogen deficiency. If this situation arises,
additional 10-20 units of nitrogen may be required when the base fertilizer is
applied at or near planting.
Seedbed Preparation
Seedbed preparation is particularly critical in the coarser textured soils.
The seedbed should be well pulverized and firm to maintain proper moisture
conditions for drilling and to insure rapid germination and emergence of the rice
plant. Although seedbed preparation is not as critical in areas where rice is not
drilled, it is still important to insure that the desired soil condition is achieved to
allow rapid emergence of the rice plant. In all situations it is important to have a
weed-free seedbed. To reduce costs, minimize the number of times a field is
cultivated before planting. Avoid “recreational” passes over the field .
STAND ESTABLISHMENT
Uniform seedling emergence and optimum seedlings per unit area are very
important in achieving good yields and quality on both main and ratoon crops.
Quality of seedbed, level of seed germination, vigor of germinating seedlings,
degree of uniform distribution of seed (both in depth and across the field), soil
moisture, soil texture characteristics, drainage, and temperature conditions all
affect stand uniformity and density. Variability in these characteristics is
responsible for the wide diversity in planting methods used across the rice belt.
Rice seed germination characteristics also dictate planting methods on some soil
types. For example, if rice seeds are covered by soil (resulting in low light) and
water (low oxygen) for extended periods, germination will not occur or will be
slow and uneven. These germination restrictions are why seedbed preparation
and soil drainage affect stand levels and uniformity. Rice can be drilled to
moisture in coarse textured soils but must be planted shallow (or uncovered) on
heavier textured soils, requiring rain or irrigation to supply moisture for
germination. Most coarse textured soils will crust when drying after being water
saturated.
The following are guides to assist farmers in achieving proper stands for
high yield and grain quality. Their experience on each field is important in getting
economical results. For example, farmers who have been successful in getting
good uniform stands consistently have had some success in reducing their
seeding rates. However, farmers need to be aware of the hazards of low
seeding rates under their conditions before taking such measures.
SEEDING DATES
The optimum seeding dates will vary by location from year to year because
of environmental conditions. Rice yields may be reduced by planting too early as
well as by planting too late. Average daily temperature at seeding is crucial in
stand establishment. The average daily temperature is calculated by adding the
daily high and low temperatures and dividing by 2. At or below 50° F, little or no
rice seed germination will occur. From 50 - 55° F, germination increases, but not
to any great extent until the temperature is above 60° F. Plant survival is not
satisfactory until the average daily temperature is above 65°. Based on this
information and seeding date research, the optimum planting dates in the region
are mid-March to late -May.
Extremely early seeding can lead to a number of problems including (1)
slow emergence and poor growth under colder conditions because of the
inherent lack of seedling vigor and cold tolerance in many varieties, (2) increased
damage from seedling diseases (predominantly water mold) under cool
conditions, (3) increased damage from birds (blackbirds, ducks and geese) which
are more numerous in the early spring, and (4) decreased activity from propanil
(herbicidal activity greatly reduced under cooler conditions). Extremely late
seedings can also be detrimental to yield. Stand establishment can be equally
difficult in hot weather. The yield potential of many varieties will decrease
significantly with later seedings. Panicle blight is thought to be associated with
higher than normal day and night temperatures during pollination and grain fill.
Late plantings are more likely to encounter these conditions. Also, many
diseases (especially blast) and insect problems are more severe, and grain
quality is often decreased with later-seeded rice
SEEDING RATES
Establishing a satisfactory stand is an essential first step in a successful
rice production program. The amount of seed necessary to accomplish this
depends primarily on the type of seeding system (dry or waterseeded) used.
Rice can be planted in three basic ways. These are water-seeded (dry or
presprouted seed dropped into a flooded field), drill-seeded (planted with a drill
on 7- to 10-inch rows) and broadcast dry (broadcast on a dry seedbed by either
ground equipment or airplane).
Regardless of the seeding system used, the desired plant stand is
constant. The optimum stand is 10 - 15 plants per square foot, while the
minimum stand is 6 - 8 plants per square foot. Rice (as most grasses) has the
ability to tiller or stool. Several head-producing shoots can be formed from one
plant. This is why a somewhat satisfactory stand can be produced from as few
as 6 - 8 seedlings per square foot if proper cultural practices are used. Stands
can be too thick as well as too thin. Excessively thick stands can often lead to
more severe disease pressure and spindly plants that may be susceptible to
lodging.
Based on this, recommendations are:
Planting on the basis of seeds per acre to obtain the desired plant
population is more accurate than planting pounds per acre. For example, 120
pounds of Bengal or Jefferson will contain fewer seeds than 120 pounds of
Cypress or Cocodrie. An ideal plant population is approximately 10 - 15 plants
per square foot. Under typical conditions, about one-half of the seed survive to
produce a plant. When water-seeding or dry broadcasting, about 100 - 150
pounds of seed per acre will be required. When drill-seeding, about 75 - 100
pounds of seed per acre will be required. Refer to plant growth regulator
section for recommendations on reduced drill seeding rates when using seed
treated with gibberellic acid. Use the higher rates when planting under less than
optimum conditions.
Considerations include:
1. Use higher recommended seeding rates when planting early in the season
when there is potential for unfavorably cool growing conditions. Cool
conditions will favor water mold (seedling disease) in water-seeded rice.
This can reduce stands. Varieties also differ in tolerance to cool growing
conditions in the seedling stage.
2. Varieties differ considerably in average seed weight. Thus, a variety with
a lower average seed weight will have more seed per pound. Producers
may want to adjust seeding rates for this factor.
3. Where seed depredation by blackbirds is potentially high, use a higher
seeding rate.
4. Where seedbed preparation is difficult and a less than optimum seedbed
is prepared, use a higher seeding rate.
5. If it is necessary to use seed of low germination percentage, compensate
with increased seeding rates. Always use high germination, certified seed
if possible.
6. When water seeding into stale or no -till seedbeds with excessive
vegetation, use higher seeding rates.
7. If any other factor exists which may cause stand establishment problems
(i.e., slow flushing capability or saltwater problems), consider it when
selecting a seeding rate.
COMMON VARIETIES
Decisions on variety selection are some of the earliest and most critical
you will make. This information will help you decide which rice varieties are best
suited to your particular growing conditions.
The varieties are grouped on the basis of grain type (long or medium).
After each variety name are lette rs in parentheses to indicate the state of origin.
The long grains are divided into two groups based on relative maturity. A brief
description of the agronomic characteristics of each of the recommended
varieties is provided. In addition to recommended varieties, descriptions of other
varieties may be included for the various maturity groups. These are varieties
that are not recommended but may be grown on limited acreage.
Recommended Long Grain Varieties
Cocodrie (LA) - Cocodrie is a very early, semidwarf long grain variety that has
displayed excellent yield potential. It is about the same height as Cypress but
has displayed somewhat better resistance to lodging. Cocodrie averages 4 - 5
fewer days to 50 percent heading than Cypress. The new variety has displayed
good second crop potential. It has displayed good milling characteristics and
good seedling vigor. Cocodrie is susceptible to sheath blight and straighthead
and moderately susceptible to blast.
Jefferson (TX) - Jefferson is a semidwarf lo ng grain that is approximately three
to four days earlier than Cocodrie. It is about the same height as Lemont
and is highly resistant to lodging. Milling yields are good, but seedling vigor is
poor. Shallow seeding and/or gibberellic acid seed treatment will enhance
establishment. Jefferson is susceptible to sheath blight and moderately
susceptible to blast. Because of the larger seed size and lower seedling vigor of
this variety, the planting rate should be increased by 15 percent.
Maybelle (TX) - Maybelle is the earliest variety recommended for Louisiana
production. Although Maybelle is not a true semidwarf, it is moderately resistant
to lodging. It displays very good seedling vigor, especially in a water-seeded
system. It has good first crop potential and excellent ratoon yield ability.
Maybelle is susceptible to blast and sheath blight.
Wells (AR) - Wells is a newly released short stature long grain variety. It has
displayed excellent yield potential in tests throughout the rice growing areas of
Louisiana. Milling yields are normally good, but Wells has demonstrated
sensitivity to low harvest moisture, resulting in lower milling yields. Seedling
vigor is excellent. The variety is similar in maturity to Cypress (1 - 2 days earlier).
Wells is 2 - 3 inches taller than Cypress but has good straw strength and stands
quite well. The variety is rated as moderately resistant to blast and susceptible to
sheath blight.
Cypress (LA) - Cypress is a semidwarf, long grain variety. It is slightly taller than
Lemont and may be slightly more susceptible to lodging. Cypress has displayed
excellent first crop yield potential and has also exhibited good second crop yield
potential. It has displayed excellent milling characteristics and extremely good
seedling vigor. Cypress is susceptible to sheath blight and blast. This variety is
also susceptible to panicle blight, a physiological disorder that causes abortion of
the developing grain.
Other Long Grain Varieties
Ahrent (AR) - Ahrent is a very early long grain variety that is slightly earlier than
Cocodrie. It has shown good yield potential and milling quality. Ahrent
is similar to Wells in plant height and appears to be similar in lodging
susceptibility. The variety is rated resistant to blast and moderately susceptible
to sheath blight. Seedling vigor appears to be good.
Drew (AR) - Drew is an early long grain variety with excellent resistance to blast
disease. It averages about 5 inches taller than Cypress and has displayed very
good yield potential. It is rated susceptible to sheath blight and moderately
susceptible to lodging. It has shown good second crop potential in limited
testing.
Jackson (TX/MS) - Jackson is closely related (sister line) to Maybelle, but it is
7 - 10 days later in maturity and 2 - 3 inches taller than Maybelle. Jackson also
has a distinctly longer flag leaf. Reactions to sheath blight and blast disease are
similar to Maybelle. Second crop potential is very good.
LaGrue (AR) - LaGrue is about 43 inches tall and moderately susceptible to
lodging. LaGrue has exhibited good yield potential. Milling yields were
variable, generally averaging less than recommended varieties in this maturity
group. LaGrue is susceptible to blast and sheath blight. Maturity is slightly
earlier than Lemont and Cypress.
Lemont (TX) - Lemont is a semidwarf that has excellent milling characteristics
but poor seedling vigor. Shallow seeding depth is essential. Because of
the short plant height and good straw strength, Lemont is highly resistant to
lodging. Lemont is very susceptible to sheath blight and susceptible to blast.
Lemont has shown very good ability to tiller (stool) and good second crop
potential.
Priscilla (MS) - Priscilla is a semidwarf early long grain variety that has shown
good yield potential. It is approximately the same height as Cypress but is
somewhat more resistant to lodging. The variety is slightly earlier than Cypress
and slightly later than Cocodrie in maturity. Priscilla is somewhat more resistant
to sheath blight than Cypress. Milling yields are fair and seedling vigor is good.
Kaybonnet (AR) - This conventional height, early long grain variety has
displayed excellent yield potential and good milling characteristics. The variety
has very high levels of resistance to most races of blast common to the south.
Kaybonnet is rated as susceptible to sheath blight disease and moderately
susceptible to lodging. It has displayed good second crop potential.
Saber (TX) - Saber is an early long grain variety that has been between Cocodrie
and Cypress in days to 50 percent heading in field testing. However, the variety
ripens quickly after heading and will reach harvest maturity in about the same
period as Cocodrie. Saber has averaged slightly lower than Cypress in grain
yield but has displayed excellent milling quality and grain appearance. Saber is
rated resistant to blast and moderately susceptible to sheath blight. The variety
is slightly taller than Cocodrie and Cypress.
Rico 1 (TX) - This variety has excellent yield potential and good milling
performance. It has typically yielded higher than other recommended medium
grain varieties in yield trials. It is a tall variety and is susceptible to lodging,
especially if nitrogen fertilization rates are too high. Seedling vigor is fair. It
ripens very slowly. It is moderately resistant to straighthead, moderately
susceptible to sheath blight and susceptible to sheath rot and blast. Short, plump
grains characterize Rico 1, making it more difficult to dry under certain
conditions. It also tends to produce chalky grains, especially under high nitrogen
fertilization. As a result, some mills may be reluctant to accept it.
XL6 (RiceTec) - XL6 is a long grain rice hybrid that has displayed very high yield
potential. Milling quality is fair to poor, and cooking quality is typical of southern
long grain varieties. Seedling vigor is excellent. XL6 is very susceptible to
lodging and is not recommended for water seeding because this increases
lodging potential. Nitrogen requirements are low, and lodging potential will be
increased when excessive nitrogen is applied. XL6 has shown high levels of
resistance to most major rice diseases.
CL121, CL141 and CFX18 are Newpath-resistant rice varieties that have
been developed for use in the Clearfield system for the control of red rice. This
system is discussed in the Weed Control section of this publication.
CL121 (LA) - CL121 is a very early, semidwarf, long grain rice variety. It has
averaged 4 - 5 days earlier than Cocodrie in days to 50 percent heading,
making it similar to Jefferson. The variety has displayed good milling yield and
quality. It is highly resistant to lodging. CL121 has shown good second
crop potential in limited testing. The variety is rated moderately susceptible to
blast and susceptible to sheath blight.
CL141 (LA) - CL141 is a tall, early long grain rice variety. It is similar in height to
Drew and rated as moderately susceptible to lodging. It is similar to Cocodrie in
maturity and has shown good second crop potential in limited testing. Grain yield
is good, and grain quality and appearance are very good. CL141 is rated
susceptible to sheath blight and susceptible to blast.
CFX18 (LA) - CFX18 is a high yielding, high quality, long grain rice variety. It is
very similar to Cypress in appearance and maturity but averages two to three
days later in days to 50 percent heading. The variety is also very similar to
Cypress in yield and milling potential, but grain size is smaller. The variety is
rated susceptible to sheath blight and moderately susceptible to blast.
Jodon (LA) - Jodon is a semidwarf, long grain variety that is a sister line to
Cypress. It has displayed good levels of resistance to lodging but may lodge
more readily than Lemont-type semidwarfs. This variety has very good
seedling vigor and excellent first and second crop yield potential. Milling yields
are generally fair to good. Jodon is susceptible to sheath blight and blast and
to straighthead. Jodon has amylographic characteristics similar to L -202, which
may make it cook slightly softer than other long grains and, thus, be unsuitable
for canning processes.
Medium Grain Varieties
Bengal (LA) - Bengal is a semidwarf variety that has displayed very good yield
potential and excellent milling quality. The milled grains are plumper than other
commonly grown medium grains in the South, a characteristic favored for some
processing uses. Seedling vigor is good, and Bengal has displayed good but
variable second crop yield potential. It is susceptible to blast and straighthead
and moderately susceptible to sheath blight. Bengal has also displayed
susceptibility to panicle blight.
Earl (LA) - Earl is a conventional medium grain variety that has displayed very
high yield potential and fair to good milling and grain appearance quality. The
variety is moderately resistant to the predominant races of blast disease. Earl
has good seedling vigor and has demonstrated good ratoon potential in limited
testing. The variety is taller than most currently grown varieties, and care should
be taken to avoid excessive rates of applied nitrogen fertilizer because this could
increase the potential for lodging.
Other Medium and Short Grain Varieties
Lafitte (LA) - Lafitte is a short-statured medium grain that is 5 - 6 days earlier in
maturity than Bengal. It is 2 - 3 inches taller than Bengal and is more susceptible
to lodging. The variety has displayed good stable yields and consistently higher
head rice yields in testing. Lafitte is resistant to the currently predominant blast
races. Seedling vigor is good and the variety has displayed good second crop
potential in limited testing. The variety is moderately susceptible to sheath blight
and susceptible to straighthead.
S-102 (CA) - S-102 is a short grain variety that is being grown on a contract basis
in Louisiana. It is very early, has good yield potential and excellent seedling
vigor. The variety is susceptible to lodging, and nitrogen rate management is
very important. Milling yields are good, but the grain can display some
chalkiness. S-102 is very susceptible to rotten neck blast disease.
Saturn (LA) - Saturn is an old (released in 1964) medium grain variety still grown
in the deep southern portions of the growing region. The variety has good
seedling vigor but is tall and extremely susceptible to lodging. Saturn has
moderate yield potential and excellent milling characteristics.
Special Purpose Long Grain Varieties
*Because of the unique characteristics of these
special purpose long grains, they should not be
commingled with standard U.S. long grain varieties.
Della (LA) - Della is an aromatic long grain that many consumers favor for its
unique aroma and taste characteristics. It is grown on limited acreage in
Louisiana. Della displays low yield potential when compared to other currently
grown varieties. Disease susceptibility is often a problem because Della is
susceptible to most major rice diseases. It is tall and is very susceptible to
lodging, even under conditions of low yield potential.
Dellrose (LA) - Dellrose is a Della-type aromatic long grain variety. It is a
semidwarf, early maturing variety that has displayed excellent grain, milling
and ratoon yield potentials. Dellrose has good aroma and a thinner grain shape
than Dellmont. Disease reaction of Dellrose is similar to Lemont. It is rated as
very susceptible to sheath blight and susceptible to blast and straighthead.
Dellmati (LA) - Dellmati is a very early, tall Basmati-type long grain. The variety
has excellent aroma and grain elongation characteristics and emulates
imported Basmati. Dellmati displays fairly low grain and milling yield and fairly
good second crop potential.
TORO-2 (LA) - TORO-2 is a special purpose, low amylose (sticky cooking) long grain, semidwarf. In taste tests, TORO-2 was judged to have acceptable TOROtype cooking and taste characteristics. TORO-2 is resistant to the predominant
blast races and moderately susceptible to sheath blight. It is also very
susceptible to straighthead.
PLANT GROWTH REGULATORS
Plant growth regulators have several applications in rice production
systems. One type of plant growth regulator can increase seedling emergence
and promote shoot elongation. Another type is used to suppress red rice seed
production in set aside or fallow acreage. Because of the specific activity of
plant growth regulators, follow label instructions and consult your county agent
before application.
Seed treatment with gibberellic acid, [GibGro (0.17 - 0.35 oz./cwt seed),
RELEASE (0.35 - 0.70 oz./cwt) or RELEASE LC (1 - 2 fl. oz./cwt)] promotes
rapid, uniform emergence in dry-seeded systems. It is especially effective on
semidwarf varieties. With gibberellic acid, seeding depth can be increased up to
3 inches to minimize flushing. In drill-seeded rice, the seeding rate can be
decreased to 75 - 85 lb./A when planting under warm conditions (daily average
temperature higher than 70° F). Under cool conditions (daily average
temperature of 60 - 70° F), the higher application rate is recommended.
Gibberellic acid [GibGro, RyzUp (0.0022 - .0066 lb. a.i./A)] is also labeled
for foliar application in Louisiana and may be beneficial in certain situations.
Follow label directions on the use of these products.
ROYAL SLO-GRO (maleic hydrazide) is labeled for red rice seed head
suppression on set aside or fallow acreage. The product should be applied at
1.5 lb. a.i./A to booting and heading red rice. Read and follow label directions.
SEEDING METHODS
Seeding methods depend on soil type, weather conditions, and producer
preferences. The main factors to consider in selecting seeding methods are
uniformity of seed distribution and seedling emergence. These factors promote
good yields as well as grain quality. There is no evidence of yield advantages for
drilled versus broadcast seeding or dry versus water seeding if stands are
adequate.
Water seeding describes sowing of dry or soaked seed into a flooded
field. It is usually implemented for any or all of the following reasons: red rice
control, wet planting season, planting efficiency and earlier crop maturity.
Water Seeding
Dry Seedbed
•
•
•
•
seedbed prepared dry before flood establishment (clear water planting).
prepare a dry seedbed in the spring, close levees immediately and apply
floodwater.
plant rice and release clear water.
less wear on equipment but possible reduced weed control.
Flooded Seedbed
•
•
•
•
•
seedbed prepared following flood establishment.
close levees and flood the field; wa ter level the field.
the floodwater must be held in the field after all water leveling or other
mechanical soil-disturbing activities have been conducted to allow for
settling of suspended materials.
plant rice and release floodwater.
increase in equipment and labor costs but better weed control.
Stale Seedbed
•
•
•
seedbed prepared three to six weeks before planting in the spring or four
to five months before planting in the fall.
may require an application of preplant burndown herbicides before
planting .
generally uses less water than the above systems at the expense of more
weeds.
No-till
•
•
•
•
•
planting directly into previous crop residue.
may require an application of preplant burndown herbicides before
planting.
generally uses less water at the expense of more weeds.
no mechanical soil disturbing allowed.
Not recommended for excessive vegetation and rutted fields
Dry seeding simply describes sowing seed into a dry seedbed by drilling
or broadcasting. This method usually offers more flexibility in planting but may
require more time to do so. This system is also weather dependent.
Conventional Seedbed
•
mechanical seedbed preparation using field cultivators and/or disk
harrows.
Stale Seedbed – see above comments
No-till – see above comments
On fine clay soils, several seeding methods can be used, including dry
and water seeding. A well-prepared, weed-free seedbed is important when rice
is dry-seeded. When dry seeding with a drill on fine clay soils, flush the field
immediately after pla nting to ensure uniform emergence. Seed can be broadcast
on a rough, cloddy seedbed if followed immediately with a flushing so soil clods
disintegrate and cover the seed. This allows good germination and uniform
emergence. Broadcast seed on a well-prepared seedbed, followed by dragging
to cover the seed, is possible in some areas. This also requires immediate
flushing of the field so that emergence is uniform. If rice is water seeded, the
seedbed may be left in a rough, cloddy condition since flushing breaks up clods
and provides some seed coverage.
Although all of these planting methods can be used for the semidwarf
varieties, experience has shown that shallow planting is much better for good
stand establishment for these varieties. For example, do not drill any deeper
than necessary on coarse soils. Although soil crusting conditions cannot always
be avoided, use proper management to prevent this condition.
EARLY FLOOD RICE CULTURE
Definitions
Two different systems are used to produce rice with early flood culture.
One system is continuous flood; the other is pinpoint flood. In the continuous
flood system, sprouted seed are dropped into a flooded field that is maintained
until near harvest. In the pinpoint system, dry or preferable sprouted seed are
dropped into floodwater. The field is drained after 24 hours and left dry for 3 - 5
days to provide oxygen and allow the roots to anchor or “peg” to the soil. Then
the flood is re-established and maintained until near harvest. For the rice plant to
continue growth, a portion of the plant must be above water by at least the fourth
leaf stage.
The advantages of applying water to a field and retaining it throughout the
growing season are: (1) easier water management and less water use, (2) red
rice and grass suppression, (3) less seedling stress from cool weather, (4)
elimination of early-season blackbird problems, (5) reduction in seedling loss due
to salt, and (6) increased nitrogen efficiency, when nitrogen is applied to dry soil
before flooding.
When a delayed flood is used, fields are drained after water seeding for
an extended period (usually 3 or 4 weeks) before the permanent flood is applied.
With this system, fertilization timing and water management after the initial
drainage are similar to dry-seeded systems.
Land preparation and stand establishment
A problem that may be encountered with both systems is the presence of
aquatic weeds late in the season and stand establishment in unlevel cuts where
water may be too deep or seed is covered with too much soil. In addition, the
continuous flood technique has the following disadvantages: (1) possibility of
seedling damage from rice seed midge, (2) seedling drift, especially in large,
open cuts, and (3) the cost of calcium peroxide coating.
Prepare land in fall or as early as possible in the spring so that vegetation
can be turned under and decompose prior to planting. This prevents oxygen
depletion during germination when the soil is flooded. Since cool water contains
more oxygen than warm water, it is desirable to plant early in the season before
floodwater gets warm.
To minimize seedling drift in the continuous flood technique, it is suggested
that the soil surface be “grooved” before flooding by pulling a spike-tooth harrow
to create ridges in the soil. A compacting groover can also be used to create
ridges. The groover compacts the soil surface to stabilize the ridges for more
uniform stand establishment and efficient field drainage. Seeds usually settle
between ridges, where they are less likely to drift.
Muddying floodwater through mechanical tillage just before applying seed
is another method for minimizing seedling drift. The suspended soil will slightly
cover and help anchor the seed. A relatively cloddy soil surface minimizes
seedling drift better than a “mirror smooth” soil surface.
Water Management
It is important to flood the soil immediately after the seedbed preparation.
A delay in flooding allows red rice and other weeds to establish before flooding,
and increases seed midge development.
Keep the area between the levees as uniformly level as possible. If the
water depth in a cut is less than 2 inches in the shallow area and greater than 6
inches in the deep area, the crop will not emerge and mature uniformly. Try to
maintain a uniform flood depth of fewer than 4 inches (1 or 2 inches is preferable)
before rice emergence. As rice gets taller, increase to 4 inches.
RICE FERTILIZATION
Generally lime is not recommended for rice production unless the pH of the
soil is 4.9 or lower. Crops grown in rotation with rice such as cotton, soybeans
and other pH sensitive crops may benefit from liming. The pH of the soil sho uld
not be increased to more than 5.8 for rice production. Overliming can induce
zinc deficiency in rice.
Phosphorus and potassium should be applied according to soil test
recommendations. On soils where phosphorus and potassium are needed, apply
preplant or before first flood. Potassium deficiency has been associated with
increase in disease incidence and severity. Fertilizer nutrients are most
efficiently used by rice when applied immediately before permanent flood
establishment. There are situations when fall application of some nutrients may
be a suitable alternative. However, neither nitrogen nor zinc should be applied in
the fall.
Rice seedlings usually show nitrogen deficiency within 15 - 25 days after
seeding, especially in soils low in organic matter. A preplant application of 15 30 pounds of nitrogen per acre is usually needed to meet the seedling nitrogen
requirement before permanent flood.
All or most of the nitrogen can be applied preplant in a water-seeded
pinpoint flood system. In a drill-seeded, dry broadcast or water-seeded delayed
flood system, all or part of the nitrogen may be applied immediately before
permanent flood. The balance of the nitrogen can be applied when deficiency
symptoms occur or anytime up to the panicle differentiation (2 mm panicle)
growth stage. Avoid applying nitrogen-containing fertilizers more than seven
days before planting.
Rice varieties may differ in their nitrogen requirements by location. Native
soil fertility, soil type and other factors determine the efficiency of nitrogen. Rice
growers should determine the N rate that provides optimum grain yield on their
land. The higher nitrogen rates within the recommended ranges for each variety
are generally required on clay soils. Avoid N deficiency and excessive N
fertilization.
Varieties vary in their nitrogen needs as follows. These recommendations
are based on multi-year, multi-location research throughout the southern region.
These rates assume proper timing.
On soil with a history of zinc deficiency, or where soil tests indicate a need
for zinc, a soil application of 7 - 8 pounds of zinc from an inorganic source (zinc
sulfate) or 1 - 2 pounds of zinc per acre as a chelate should be made. Zinc can
be applied foliarly at the rate of 0.5 - 1.0 pound per acre as a chelate. Sulfur may
be needed at a rate of 20 - 25 pounds per acre where large amounts of soil have
been moved in land leveling. Sulfur deficiencies resemble nitrogen deficiencies,
producing pale yellow plants that grow slowly. If these symptoms appear,
applying 100 pounds of ammonium sulfate per acre will provide 21 pounds of
nitrogen and 24 pounds of sulfur per acre.
RATOON CROP
Certain climatic conditions along with the early maturity of commonly
grown varieties allow for a second or ratoon crop during a single growing season.
This ratoon crop is produced from the re-growth of the previously harvested crop.
Weather is a critical factor when determining how successful a ratoon crop
will be. Mild conditions will speed second crop maturity. Later than normal frostdates will also aid in producing a second crop. This explains the success of
ratoon crops in southern Louisiana and why Arkansas does not ratoon crop.
Fertility is the major cultural management practice of the second crop.
Ratoon rice should be fertilized with 45 - 75 pounds of nitrogen per acre when
first crop harvest is before August 15. When the first harvest is after August 15,
fertilize with 30 - 45 pounds of nitrogen per acre. When conditions appear
favorable for good second crop production (minimal field rutting, little or no red
rice, healthy stubble), apply the higher rate of nitrogen. Apply nitrogen and
establish a shallow flood within five days after harvest. When the main crop is
harvested after August 15, the potential for profitable second crop production is
reduced because of the increased likelihood of unfavorable weather.
Broadleaf weeds such as dayflower may become a concern in ratoon rice.
See weed control section for herbicide recommendations.
CROP ROTATION
Several crops can be used in rotation with rice. Soybean is one of the
more popular throughout the region. Wheat can be seen in Arkansas. Cotton is
also an option for Northeast Louisiana and parts of Mississippi. To a lesser
degree, corn and sorghum are used as rotations.
Some farmers do not choose to rotate. Continuous rice culture can
worsen weed problems such as red rice. Since growers aren' t rotating into
soybeans, they cannot rotate herbicides that help fight red rice. Mississippi State
University weed scientist Mark Kurtz conducted an eight-year study evaluating
rice-soybean rotation patterns. After the third year of continuous rice, yields
dropped off significantly and never rebounded.
Aquaculture rotations such as rice/crawfish/rice are often utilized in
Louisiana with as many as 30,000 acres in such a rotation.
WORKER ACTIVITIES
Land Preparation – This information can be obtained from the ‘Crop Production’
section of this report. When operating mechanical equipment there is a very
slight risk of operator injury when dealing with the manual adjustment of the
plowing equipment - tightening of bolts, etc. With a wrench, an operator could
bruise the knuckles if the wrench were to slip - only a minor injury.
Planting Methods –This information can be obtained from the ‘Crop Production’
section of this report. Only rare cuts, scrapes, and bruises would occur in the
adjustment of planting equipment. It would be likened to the carpenter who
occasionally hits his thumb with a hammer - only a minor injury.
Cultivation – Cultivation practices prior to planting are covered in the ‘Crop
Production’ section of this report. Due to the growth habit and flood culture of
rice, mechanical cultivation after planting does not exist.
Fertilization/Pesticide Application – This information can be obtained from the
‘Crop Production’ section of this report. Take necessary precautions in handling
fertilizers, lime, etc.
At one time, flaggers were used to assist in aerial application of pesticides.
However, with the advent of GPS (Global Positioning System) tracking systems,
flaggers are rarely, if ever, used. The only time an operator would come in
contact with pesticides is when loading the spray equipment, i.e., the spray tank
of the equipment. Assuming proper PPE, risk is minimal.
Approximately 75-85% of all pesticides are applied by air. Roughly 2025% is still applied by land. Pre-plant incorporated herbicides are applied with
ground equipment.
Irrigation – Irrigation in rice is essentially managing or maintaining the
floodwater. This is accomplished through pumping coupled with ditch, canal, and
levee management.
Scouting – The only time workers are in the field and not on a piece of heavy
machinery usually involves pest monitoring. ATV’s (all terrain vehicles) are
frequently used to assist with insect, weed, and disease monitoring as well as
flood control. Conceivably a worker could have an injury involving an ATV.
However, the speed at which one travels in a rice field is so slow, injury rarely if
ever happens.
Harvesting – Premature harvesting of rice keeps the grain from reaching
maturity, and can cause serious losses in the quality of the product.
Furthermore, it is important to accomplish the harvest while the moisture content
of the grain is acceptable. Using moisture sensors, the moisture content should
be 17 - 22%. Too low a moisture content can cause the panicles to shatter at the
time of cutting leading to serious losses of product.
Combine harvesters or simply ‘combines’ are machines that do the cutting,
threshing and pre-cleaning of the rice in one operation. Self-propelled with an
enclosed and often temperature regulated cab, combines have a cutting
apparatus, a threshing chamber composed of a revolving threshing drum (with
teeth), and a stationary counter-thresher. Two major types are used: a
conventional setup and a stripper-header. There are variances among augers
and feeding mechanisms among the two. Generally the stripper-header offers
considerably faster harvesting, but it does have drawbacks. It is more expensive,
heavier to operate, and is limited to small grains (rice, wheat, oats, etc.) This
makes it difficult for a grower who wishes to use the same combine for another
crop such as soybeans in rotation with rice.
Generally, a minimum of 4 - 5 people are involved in rice harvesting: one
to operate the combine, one to drive a grain cart, and two or more to drive the
trucks to the grain elevator for drying and storage in bins. Depending on
equipment used and field conditions, 25 - 50 acres may be harvested in one day.
There are times when the combine will become clogged and require
manual removal of debris from the header or cutter mechanism. Cuts, bruises,
and abrasions can occur as a result. In rare cases, a fatality can occur when an
operator, who does not properly shut off the header mechanism, attempts to
remove debris from the header. This occurred more often in years past, but due
to more safety features of the equipment, including automatic shutoff devices,
fatalities are rare. Institutions that gather agricultural statistics such as the USDA
and NIOSH (The National Institute for Occupational Safety and Health) do not
carry data specific to rice combine injuries and fatalities. However, state rice
specialists agree the occurrence of fatalities involving rice combines is declining.
INSECTS
Insects can be a major factor limiting rice production in Louisiana. The rice
water weevil and the rice stink bug are key pests. They cause significant
reduction in the quantity and quality of rice produced each year. Other insects
attacking rice, though not key pests, can occasionally reduce rice yield and
quality significantly. These include the rice seed midge, rice leaf miner, fall
armyworm, chinch bug, rice stalk borer, and sugarcane borer.
This section contains information about the identification, life cycle, injury
to rice, and current scouting and management practices for these pests. The
scouting and management recommendations are based on the best available
information and will be modified as additional research is conducted. Rice insect
control recommendations are summarized in this section, but consult your county
agent to get the latest recommendations for specific insect pests.
Rice Water Weevil, Lissorhoptrus oryzophilus (Kuschel)
Description and Life Cycle: The rice water weevil is one of the most injurious
insect pests in rice production. Yield losses of more than 1,000 pounds per acre
can occur from severe infestations. Rice water weevil adults are grayish brown
beetles about 1/8 -inch long with a dark brown V-shaped area on their backs.
They overwinter as adults in grass clumps and ground debris near rice fields.
Wing muscles of overwintering adults degenerate so these insects cannot fly.
When spring temperatures rise to 65° F, wing muscles begin to regenerate and
adults begin moving out of overwintering sites. Adults fly in the early evening,
with little flight occurring when night temperatures fall below 60° F.
Adults will invade either unflooded or flooded rice fields and begin feeding
on the leaves of rice plants. The flight muscles degenerate again as the weevils
become established, and the adults cannot fly. Females begin egg laying in
flooded fields or in areas of unflooded fields that contain water, such as low
spots, potholes or tractor tire tracks. Females deposit white, elongate eggs in the
leaf sheath at or below the waterline. White, legless, C-shaped larvae with small
brown head capsules emerge from the eggs in about seven days.
First instar larvae are about 1/32 inch long and feed in the leaf sheath for a
short time before exiting the stem and falling through the water to the soil.
Afterwards, they burrow into the mud and begin feeding on the roots of rice
plants. The larvae continue to feed in or on the roots of rice plants developing
through four instars in about 27 days. Larvae increase in size with each
succeeding molt. Fourth instar larvae are about 3 /16 inch long. Larvae pupate in
oval, watertight cocoons attached to the roots of rice plants. The cocoons are
covered with a compacted layer of mud and resemble small mud balls.
Adults emerge from the cocoons in 5 - 7 days, are able to fly a short time
after emerging and may attack rice in the same or a different field. The life cycle
from egg to adult takes about 35 days. The length of the life cycle is
temperature-dependent, however, and can vary from 25 - 45 days in warm and
cool weather, respectively. The number of generations per year varies with
latitude. Two and a partial third generation can occur in the southern ricegrowing areas of the region. One and a partial second generation occur in the
northern rice growing areas. Most adult weevils emerging in late July to early
August fly to overwintering sites and remain inactive until the next spring.
Injury: Adult rice water weevils feed on the upper surface of rice leaves, leaving
narrow longitudinal scars that parallel the midrib. Adult feeding injury can kill
plants when large numbers of weevils a ttack very young rice, but this is rare and
is usually localized along the field borders. Larvae feeding in or on rice roots
cause most economic injury. This feeding or root pruning reduces root surface
area, resulting in decreased nutrient uptake by the plant. Plants with severely
pruned root systems turn yellow and appear to be nitrogen deficient. At harvest,
plants from heavily infested fields will be shorter than normal and have lower
yields. Each larva found in a 4-inch (diameter) by 3-inch (deep) core sample
reduces rice yield by 40 pounds per acre.
Scouting and Management: With the loss of carbofuran as a chemical control
for rice water weevil in rice, larval counts are no longer used as a sampling
procedure. Icon as a preventative seed treatment is a newer insecticide
now used against larvae. If Icon is not used, upon sampling the field, any
presence of an adult rice water weevil warrants spraying of a foliar insecticide if
conditions are favorable for oviposition. Foliar insecticides such as Karate Z and
Fury are labeled for use and should be aimed to kill adults before they lay eggs.
Most of oviposition occurs when there is water in the field. Therefore, control is
recommended when: (1) Adults are present, and (2) there is water in the field
(flood), or there will be water soon. Previous research also indicates that you
can apply Karate Z when adults or fresh feeding scars are present within 24
hours before permanent flood and still obtain good control.
Management of the Rice Water Weevil using Cultural Control: Fields may be
drained to reduce rice water weevil numbers. Draining fields is the only rice
water weevil control method available for rice grown in rotation with crawfish.
This procedure requires careful planning so conflicts with weed, disease and
fertilizer management programs can be avoided or minimized
The Stem Borers
Rice Stalk Borer, Chilo plejedellus (Zink)
Description and Life Cycle: The rice stalk borer is a sporadic pest of rice in the
south. These borers overwinter as last instar larvae in the stalks of rice and
other host plants. Larvae pupate in the spring, and adult moths emerge in early
to late June, mate and live on various hosts until rice stem diameter is
large enough to support tunneling larvae. Adults are about 1 inch long with pale
white fore and hind wings tinged on the edges with metallic gold scales. Front
wings are peppered with small black dots. Although egg laying may begin in late
May, injurious infestations usually occur from August through September. Flat,
oval cream-colored eggs are laid in clusters of 20 - 30 on the upper and lower
leaf surfaces. Eggs are laid at night over 1 - 6 days. Larvae emerge in four to
nine days and crawl down the leaf toward the plant stem. Larvae may feed for a
short time on the inside of the leaf sheath before boring into the stem. They are
pale yellow-white with two pairs of stripes running the entire length of the body.
These stripes distinguish rice stalk borer larvae from sugarcane borer larvae,
which have no stripes. Mature larvae are about 1 inch long. Larvae move up
and down the stem feeding for 24 - 30 days before moving to the first joint above
the waterline, chewing an exit hole in the stem and constructing a silken web in
which to pupate. Pupae are about 1 inch long, brown and smoothly tapered.
There are two to three generations per year in rice.
The Sugarcane Borer, Diatrea saccharalis (F.)
Description and Life Cycle: The sugarcane bore is also a sporadic pest of rice
in the south. Like the stalk borer, sugarcane borers overwinter as last instar
larvae in the stalks of rice and other plants. These larvae pupate in the spring,
and adult moths emerge as early as May. They mate and live on various hosts
until rice stem diameter is large enough to support larval feeding. Adults are
straw-colored moths about 1 inch long with a series of black dots, arranged in a
V-shaped pattern, on the front wings. Egg laying on rice can begin as early as
May, but economically damaging infestations generally do not occur until August
or September. The flat, oval, cream-colored eggs are laid at night in clusters of 2
- 100 on the upper and lower leaf surfaces over 1 - 6 days. Larvae emerge in 3 5 days, crawl down the leaf and bore into the plant stem. They move up and
down the stem, feeding for 15 - 20 days before chewing an exit hole in the stem
and pupating. Larvae are pale yellow-white in the summer, with a series of
brown spots visible on the back. Overwintering larvae are a deeper yellow and
lack the brown spots. The lack of stripes distinguishes sugarcane borer larvae
from rice stalk borer larvae, which have stripes in winter and summer. Mature
larvae are about 1 inch long and do not enclose themselves in a silken web
before pupation. The pupae are brown, about 1 inch long and roughly cylindrical
in shape, not smoothly tapered, as are rice stalk borer pupae. Overwintering
sugarcane borer larvae are usually found closer to the plant crown than rice stalk
borer larvae. The pupal stage lasts 7 - 10 days. There are 3 generations per
year.
Injury: Injury to rice results from stalk and sugarcane borer larvae feeding on
plant tissue as they tunnel inside the stem. Injury is often first noticed when the
youngest partially unfurled leaf of the plant begins to wither and die, resulting in
a condition called deadheart. Later in the growing season, these rice stems are
weakened and may lodge before harvest. Stem feeding that occurs during
panicle development causes partial or complete sterility and results in the
whitehead condition. The white, empty panicles are light in weight and
stand upright.
Scouting and Management: Unfortunately, by the time signs of field
infestations (deadhearts, white-heads) are noticed, it is usually too late to apply
effecti ve chemical treatments. A seed treatment of Icon 6.2FS at 0.025 - 0.05 lb.
a.i./A prior to planting is an effective control up to the panicle differentiation
stage. For foliar sprays to be effective after crop emergence, you must time
application when larvae are small before they enter rice stalks. Once larvae
enter the stalks, pesticides are not effective. Extensive scouting of rice fields is
required to time pesticide applications properly. Scouting can be conducted for
stem borer adults or egg masses. Eggs are laid over an extended period, and
although some injury may be prevented, satisfactory control using chemical
treatments is difficult and has not been generally successful. Stem borer eggs
and larvae are parasitized by the wasps, Trichogramma minutum (Riley) and
Agathis stigmaterus (Cresson). It is believed these parasites play an important
role in maintaining stem borer numbers below economic levels.
Rice Stink Bug, Oebalus pugnax (F.)
Description and Life Cycle: Adult rice stink bugs are shield -shaped, metallicbrown insects about ½ inch long. Rice stink bugs overwinter as adults in grass
clumps and ground cover. They emerge from overwintering sites in early spring
and feed on grasses near rice fields before invading fields of maturing rice.
Adults live 30 - 40 days. Females lay masses of light-green cylindrical eggs on
the leaves, stems, and panicles of rice plants. Eggs are laid in parallel rows with
about 20 - 30 eggs per mass. As they mature, eggs become black with a red tint.
Immature stink bugs (nymphs) emerge from eggs in 4 - 5 days in warm weather
or as long as 11 days in cool weather. Nymphs develop through 5 instars in 15 28 days. Newly emerged nymphs are about 1/16 inch long, with a black head and
antennae and a red abdomen with 2 black bars. Nymphs increase in size with
successive molts and the color of later instars becomes tan-green. Four
generations per year can occur in the south - 2 on weed hosts and 2 on rice.
However, only 1 generation usually develops in a give n field .
Injury: Rice stink bugs feed on the rice florets and developing rice kernels.
Feeding on florets reduces rough rice yields, but most economic loss results from
stink bugs feeding on developing kernels. Kernel feeding results in discolored or
“pecky” rice kernels that have lower grade and poor milling quality. Both adult
and nymph rice stink bugs feed on developing rice grains, but adults alone
account for most economic losses in rice. Relationships between stink bugs and
stink bug injury developed in Texas show a strong increase in percentage of
pecky rice and a strong decrease in percentage of head yield with increasing
numbers of adult stink bugs during the heading period. When numbers of
immature stink bugs were included, this relationship did not change.
Scouting and Management: Several natural enemies are important in
reducing rice stink bug numbers in rice. Adults and nymphs are parasitized by
the flies, Beskia aelops (Walker) and Euthera tentatrix (Lav.). Rice stink bug
eggs are parasitized by the tiny wasps, Oencyrtus anasae (Ashm.) and
Telonomus podisi (Ashm.). Management relies significantly on the activity of
these naturally occurring biological control agents. Insecticidal control based on
the results of field scouting is recommended when rice stink bugs escape from
the control provided by natural enemies.
Rice fields should be sampled for stink bugs using a 15-inch diameter
insect sweep net once each week beginning immediately after pollination and
continuing until kernels harden. Do not sample fields at midday when stink bugs
may be seeking shelter from the heat in the shade at or near the ground. Avoid
sampling field borders, where stink bug numbers are often higher than in the field
interiors. A sample consists of 10 consecutive 180-degree sweeps made
while walking through the field. Hold the net so that the lower half of the opening
is drawn through the foliage. After 10 successive sweeps, count the number of
rice stink bug nymphs and adults. Normally 10 samples of 10 sweeps each
are made per field. Alternatively, 100 random sweeps may be taken per field.
During the first two weeks of heading, fields averaging one or more rice stink
bugs per three sweeps (30 or more per 100 sweeps) should be treated with an
insecticide. After the first two weeks of heading, treat fields when an average
one or more stink bugs per sweep (100 or more per 100 sweeps) is found.
Rice Seed Midge, Chironomus spp.
Description and life cycle: Adult midges can be seen in swarms over rice
fields, levees, roadside ditches, and other bodies of water. Adult midges
resemble small mosquitoes but lack the needle-like mouthparts. They hold their
forelegs up when resting. Eggs are elongate and laid in strings, usually on the
surface of open water. A sticky material that forms a gelatinous coat around the
eggs holds the strings together. After emerging, the larvae move to the soil
surface, where they live in spaghetti-like tubes constructed from secreted silk,
plant debris and algae. The la rvae go through 4 instars before pupating under
water in the tubes. The life cycle from egg to adult requires 10 - 15 days.
Injury: Midge larvae injure rice by feeding on the embryo of germinating seeds
and on the developing root and shoot of young rice seedlings. Most economic
injury to rice is the result of stand loss caused by larvae feeding on the embryo of
germinating seeds. Reports of injury caused by rice seed midge have increased
in recent years.
Scouting and Management: Rice seed midge is a problem only for rice seeds
and seedlings in water-seeded fields. Midges are not a problem in rice more
than 2 - 4 inches tall. Scout fields for midges and midge injury within 5 - 7 days
after seeding. Repeat scoutings at 5- to 7-day intervals until rice seedlings are
about 3 inches tall. Larval tubes on the soil surface indicate midge presence.
There are many midge species, most of which do not attack rice, and the
presence of midge tubes alone does not indicate the need to treat a given field.
Midge injury is indicated by the presence of chewing marks on the seed,
roots and shoots and by the presence of hollow seeds. If midge injury is
present, and plant stand has been reduced to fewer than 15 plants per square
foot, treatment may be necessary. One available cultural method for control of
rice seed midge is to drain fields to reduce numbers of larvae. Re -seeding of
heavily infested fields may be necessary. The potential for damaging levels of
seed midge can be reduced or prevented by using recommended water and crop
management practices. Holding water in rice fields for more than 2 - 3 days
before seeding encourages the buildup of large midge numbers before seeding
and should be avoided. Practices that encourage rapid seed germination a nd
seedling growth, such as using pre-sprouted seed and avoiding planting in cool
weather, will help to speed rice through the vulnerable stage and reduce the
chances for serious damage.
Chinch bug, Blissus leucopterus leucopterus (Say)
Description and life cycle: Chinch bugs overwinter as adults in grass clumps,
leaf litter and other protected areas, emerging in early- to mid-spring to feed and
mate on grass hosts including small grains such as wheat, rye, oats and barley.
Adults are small, black insects about 1/ 8 inch long, with white front wings. Each
wing has a triangular black spot near the outer wing margin. Adults lay white,
elongate eggs 1/24 inch long behind the lower leaf sheaths or in the soil near the
roots. Eggs turn red as they mature and larvae emerge in 7 - 10 days. There are
5 nymphal instars. Early instar nymphs are red with a yellow band on the front
part of the abdomen. Last instar nymphs are black and gray with a conspicuous
white spot on the back. The life cycle from egg to adult takes 30 - 40 days, and
adults may live 2 - 3 weeks.
Injury: Chinch bugs are a sporadic pest of rice in the south. Economic injury to
rice generally occurs when favorable weather conditions and production
practices allow chinch bugs to build in corn, sorghum, and wheat fields. As these
crops mature and are harvested, large numbers of chinch bugs may move to
young plants in nearby rice fields. Serious economic losses can result from
chinch bug infestations if thresholds are reached. The trend toward increasing
acreage of small grains increases the potential for chinch bug problems. Chinch
bug injury results when adults and nymphs feed on the leaves and stems
of rice plants. Feeding on young seedlings causes leaves and stems to turn light
brown. High numbers of chinch bugs can kill young plants, severely reducing
plant stands.
Scouting and Management: Check unflooded rice near small grain fields every
3 - 5 days from seedling emergence until application of permanent flood. Check
foliage in rice fields for chinch bugs. Thresholds for chinch bugs in rice are not
available. If high numbers of chinch bugs are present and plant stands are being
reduced, the field should be treated. Cultural and chemical control methods are
available. Cultural control consists of flooding infested fields to kill chinch bugs
or to force them to move onto rice foliage where they can be treated with an
insecticide. This tactic requires that levees be in place and that rice plants be
sufficiently large to withstand a flood. Cultural control may be more expensive
than chemical control.
The Fall Armyworm, Spodoptera frugiperda (J. E. Smith)
Description and Life Cycle: The fall armyworm feeds on most grasses found in
and around rice fields. It is also a serious pest of corn and pasture grasses.
Since rice is not its preferred host, the fall armyworm is only an occasional pest
on rice. Adult moths are about 1 inch long with gray-brown sculptured front
wings and whitish hind wings. The front wings of male moths have a white bar
near the wing tip. This bar is absent in female moths. Females lay masses of 50
to several hundred whitish eggs on the leaves of rice and other grasses in and
around rice fields. Egg masses are covered with moth scales and appear fuzzy.
The larvae emerge in 2 - 10 days, depending on temperature, and begin
feeding on rice plants. They vary from light green to brown to black, but have
distinctive white stripes along the side and back of the body. Larvae feed for two
to three weeks, developing through 4 instars. Mature larvae are about 1 inch
long and have a distinctive inverted “Y” on the head. Mature larvae prepare a
cocoon and pupate in soil or decomposing plant material. Moths emerge in 10 -
15 days, mate and disperse widely before laying eggs on new plants. At least 4
generations per year occur in Louisiana.
Injury: Fall armyworm larvae feed on the leaves of young rice plants, destroying
large amounts of tissue. Leaf loss of 25 percent in the seedling stage can reduce
rice yields by about 130 pounds per acre. When large numbers of armyworms
are present, seedlings can be pruned to the ground, resulting in severe stand
loss. Fall armyworm infestations generally occur along field borders, levees and
in high areas of fields where larvae escape drowning. The most injurious
infestations occur in fields of seedling rice that are too young to flood. Larvae
from the first overwintering generation, occurring in early spring, are the most
injurious. Infestations later in the season may cause feeding injury to rice
panicles, although this is rare.
Scouting and Management: After germination of seedlings, scout fields weekly
for larvae on plants. Sample plants every 10 feet along a line across the field,
and repeat this process in a second and third area of the field. Treat when there
is an average of 1 armyworm per 2 plants. Fall armyworm management consists
of cultural, chemical and biological control. Parasitic wasps and pathogenic
microorganisms frequently reduce armyworm numbers below economical levels.
Bacillus thuringiensis var. kurstaki under various trade names (Javelin, Biobit)
can also suppress populations. Since adults lay eggs on grasses in and around
rice fields, effective management of grasses can reduce larval infestations.
When fall armyworm numbers reach threshold levels, cultural or chemical control
is needed. Cultural control consists of flooding infested fields for a few hours to
kill fall armyworm larvae. This requires that levees be in place and that rice
plants be large enough to withstand a flood. Cultural control may be more
expensive than chemical control.
The Rice Leaf Miner, Hydrelia griseola (Fallen)
Description and Life Cycle: Adults are dark flies with clear wings and a
metallic blue-green to gray thorax. Less than 1/4 inch long, they can be seen
flying close to the water and lighting on rice leaves. White eggs are laid singly on
rice leaves that float on the water. Transparent or cream-colored legless larvae
emerge in 3 - 6 days and begin feeding between the layers of the rice leaf.
Larvae become yellow to light green as they feed. Mature larvae are about 1/4
inch long. The larvae feed for 5 - 12 days before pupating. Adults emerge after
5 to 9 days and live 2 - 4 months. Under ideal conditions the life cycle can be
completed in as little as 15 days. In cool weather the life cycle can extend for
more than 1 month.
Injury: The rice leaf miner is a sporadic problem in Louisiana. Problems are
more severe in continuously flooded rice tha n in periodically flooded rice, and
when water is more than 6 inches deep. Injury is usually greatest on the upper
side of levees where water is deepest. The rice leaf miner attacks rice during the
early spring. Larvae feeding between the layers of the rice leaf cause injury.
Leaves closest to the water are attacked and killed. As larvae move up the plant,
additional leaves die. When leaf miner numbers are high, entire plants can die,
reducing stands severely. In Louisiana, the rice leaf miner seems to attack fields
in the same vicinity year after year.
Scouting and Management: Scout fields for rice leaf miners by walking through
flooded rice fields and gently drawing the leaves of rice plants between the
thumb and forefinger. Bumps in the leaves indicate the presence of leaf miner
larvae or pupae. If leaf miners are present and plant numbers are reduced to
less than 15 per square foot, treatment is necessary. Rice leaf miner
management involves cultural control or insecticide application, perhaps both.
Maintaining water depth at 4 - 6 inches will usually prevent problems with rice
leaf miner. If leaf miners are present, lowering the water level in rice fields so
that rice leaves can stand up out of the water also will help to prevent injury.
Other Insect Pests of Rice: Several other insects may occasionally attack rice
in Louisiana. They include the southern green stink bug, Nezara viridula (L.),
several grasshopper species, and the larvae of several species of skippers and
tiger moths. The numbers of these insects in rice fields are usually below levels
justifying treatment, but they may increase rapidly under favorable conditions and
yield losses can occur.
RECOMMENDATIONS FOR
CONTROL OF INSECTS ON RICE
Insecticide1
Insect
2
Aphids
Armyworms
Karate Z
3
Fury
4
Chinch bugs
Methyl parathion
5
4EC
2
Karate Z
3
Fury
6
Icon 6.2 FS
2
Grasshopper
Rice leaf
miners
Karate Z
3
Fury
Methyl parathion
5
4EC
2
Karate Z
3
Fury
Methyl parathion
5
4EC
Dosage Per
Acre (Active
Ingredient)
0.025 - 0.04 lb
0.04 - 0.05 lb
PreHarvest
Interval
21 days
14 days
0.5 - 0.75 lb
15 days
0.025 - 0.04 lb
0.04 - 0.05 lb
0.025 - 0.05 lb
21 days
14 days
0.025 - 0.04 lb
0.033 - 0.05 lb
0.5 lb
21 days
14 days
15 days
0.025 - 0.04 lb
0.04 - 0.05 lb
0.75 lb
21 days
14 days
15 days
Comments
Treat when stand is
threatened, aphids are
present, and natural control is
non-sufficient.
Treat when there is one
armyworm per two plants.
Seed treatment with Icon for
suppression only. Obtain
treated seed from authorized
seed dealer. Adjust seeding
rate based on seed treatment
rate to obtain 0.025-0.05
lbs/A.I./acre.
For foliar sprays: Flood fields
first.
Apply when eggs and larvae
are abundant on seedling rice
7
1.56 lb
7
0.6 - 0.9 lb
1 - 1.25 lbs
(2 - 2.5 pts
liquid)
0.5 - 0.75 lb
7 days
14 days
0.025 - 0.04 lb
0.033 - 0.05 lb
0.025-0.05 lb
21 days
14 days
0.025-0.04 lb
0.04-0.05 lb
21 days
14 days
0.125-0.25 lb
80 days
Malathion 57% EC
Rice stink
bugs
Rice water
weevil
(larvae)
Malathion 57% EC
Carbaryl
Methyl parathion
5
4EC
2
Karate Z
3
Fury
6
Icon 6.2 FS
2
Rice water
weevil
(adults)
Karate Z
3
Fury
Rice water
weevil
(eggs)
Rice seed
midges
Dimilin 2L
8
6
Icon 6.2 FS
7 days
15 days
0.025-0.05 lb
and/or when stands are being
reduced to less than 15
plants per square foot.
Scout in the morning for best
results. Treat when there are
30 stink bugs per 100 sweeps
during first two weeks of
heading. Treat when there
are 100 stink bugs per 100
sweeps later until two weeks
before harvest.
Seed treatment. Obtain
treated seed from authorized
seed dealer. Adjust seeding
rate based on seed treatment
rate to obtain 0.025-0.05
lbs/A.I./acre.
Check 10 locations every 3-4
days. Treat when adults are
present or fresh feeding scars
are observed and when
conditions are favorable for
egg-laying (i.e. water is
present or will be present
soon). Scout again beginning
5-7 days after application.
More than one application
may be necessary.
A flood is required. Do not
apply if flooding is in
progress.
Seed treatment (see above).
For non Icon-treated fields
9
see footnotes
1
Insecticides are not listed in order of effectiveness.
2
Do not use treated rice fields for the aquaculture of edible fish and crustaceans. Do not release
floodwater within seven days of application. Do not apply more than 0.12 lb A.I./acre/season. Do
not apply as ultra-low volume (ULV) spray.
3
Do not use treated rice fields for the aquaculture of edible fish and crustaceans. Do not release
floodwater within seven days of application. Do not make applications less than seven days apart.
Do not apply more than 0.2 lb A.I./acre/season. Do not apply as ULV spray.
4
Flooding is effective for armyworm control if plants are sufficiently developed.
5
Do not use methyl parathion within 14 days of applying propanil.
6
Allow 100-ft buffer between Icon seeded field and crawfish ponds. Do not release floodwater into
crawfish ponds. For water-seeded rice, do not release planting flood water prior to 24 hours after
seeding. Do not plant leafy vegetables within one month following planting of treated rice seed.
Do not plant root crops within five months following planting of treated seed. Do not plant small
grains, other than rice, within twelve months after planting treated seed.
7
Do not use Malathion within 15 days of applying propanil. Applications may not be made around
bodies of water where fish or shellfish are grown or harvested commercially.
8
Do not use treated rice fields for the aquaculture of edible fish and crustaceans. Use at least 5
gallons total volume per acre. Do not disturb flood for at least 7 days after application. Do not
release floodwater within 14 days of application.
9
For non-Icon treated fields: Water management. Check fields for damage during first week after
planting. If stands are being reduced significantly (less than 15 plants per square foot), drain and
replant if necessary.
WARNING: Always read the label for additional information. Re-entry times for workers entering
treated fields should be strictly observed. Be sure to check the label for this information.
RICE INSECT CONTROL IN RICE/CRAWFISH ROTATION FIELDS
Insect
Insecticide1
Armyworms B.t. (Bacillus
1
thuringiensis)
2
Rice leaf
Malathion 57% EC
miners
Dosage Per
Acre (Active
Ingredient)
0.5 lb
PreHarvest
Interval
0
1.56 lb
7 days
0.6 - 0.9 lb
7 days
Rice seed
midges
Rice stink
bugs
Rice water
weevil
2
Malathion 57% EC
Comments
Treat when there is one
armyworm per two plants.
Apply when eggs and larvae
are abundant on seedling
rice and/or when stands are
being reduced to less than
15 plants per square foot.
Water Management. Check
fields for damage during first
week after planting. If stands
are being reduced
significantly (less than 15
plants per square foot),
drain and replant if
necessary.
Scout in the morning for
best results. Treat when
there are 30 stink bugs per
100 sweeps during the first
two weeks of heading. Treat
when there are 100 stink
bugs per 100 sweeps later
until two weeks before
harvest.
Water Management. Two to
three weeks after permanent
flood, sample for rice water
weevil larvae. If populations
are five larvae per core,
drain the field and allow the
field to dry two to three
weeks. (This allows soils to
dry to the point of cracking).
1
There are several formulations on the market. Follow label directions.
2
Do not use Malathion within 15 days of applying propanil. Applications may not be made around
bodies of water where fish or shellfish are grown or harvested commercially.
WARNING: Always read the label for additional information. Re-entry times for workers entering
treated fields should be strictly observed. Be sure to check the label for this information.
DISEASES
Introduction
Disease damage to rice can greatly impair productivity and sometimes
destroy a crop. The United States does not have any of the destructive viral
diseases present in other rice-growing areas of the world, but fungal diseases
are prevalent and very destructive to Louisiana rice. Several bacterial diseases
have been found, but only one is associated with any significant yield losses.
Direct losses to disease include reduction in plant stands, lodging, spotted
kernels, fewer and smaller grains per plant, and a general reduction in plant
efficiency. Indirect losses include the cost of fungicides used to manage disease,
application costs, and reduced yields associated with special cultural practices
that reduce disease.
Bacterial Leaf Blight
Bacterial leaf blight is caused by the bacterium Xanthomonas campestris
pv. oryzae. It was first identified in the United States in Texas and Louisiana in
1987. No major losses have been associated with this disease in the United
States, but bacterial leaf blight in other parts of the world causes severe damage.
The blight bacterium overwinters in rice debris in the soil and on weed hosts.
There is also a slight chance that seed may transmit the pathogen. The
pathogen is spread by wind-blown rain, irrigation water, plant contact and
probably on plant debris adhering to machinery. High humidity and storms favor
disease development. Watersoaked areas appear on the leaf margins near the
tips, enlarge and turn white to yellow. As the lesions mature, they expand, turn
white and then gray because of growing saprophytic fungi. The lesion may be
several inches long. Accurate identification is important since the symptoms can
be confused with other diseases, especially leaf scald, herbicide damage, and
other plant stress. Management practices include rotating to non-grass crops,
tilling to destroy plant debris, and avoiding contaminating the field through
infected plant materials or irrigation water.
Blast
The fungus Pyricularia grisea causes Rice blast. The disease is also
called leaf blast, node blast, panicle blast, collar blast, and rotten neck blast;
depending on the portion of the plant affected. Blast has been one of the most
important diseases in the south, causing considerable yield losses to susceptible
varieties under favorable environmental conditions.
Blast can be found on the rice plant from the seedling stage to near
maturity. The leaf blast phase occurs between the seedling and late tillering
stages. Spots on leaves start as small white, gray, or blue tinged spots. These
enlarge quickly under moist conditions to either oval, diamond-shaped spots or
linear lesions with pointed ends containing gray or white centers and narrow
brown borders. Leaves and whole plants are often killed under severe
conditions. Lesions on resistant plants are small brown specks that do not
enlarge.
On stem nodes, the host tissue turns black and becomes shriveled and
gray as the plant approaches maturity. The infected area may turn dark purple to
blue-gray because of the production of fungal spores. Culms and leaves become
straw-colored above the infected node. Plants lodge or break off at the infected
point, or they are connected only by a few vascular strands. Some varieties are
infected where the flag leaf attaches to the sheath at the collar. The lesion turns
brown to gray, and the flag leaf becomes detached from the plant as the lesion
area becomes dead and dry.
Rotten neck symptoms appear at the base of the panicle starting at the
node. The tissue turns brown and shrivels, causing the stem to snap and lodge.
If the panicle does not fall off, it may turn white to gray, or the florets that do not
fill will turn gray. Panicle branches and stems of florets also have gray-brown
lesions.
Scouting a field for blast should begin early in the season during the
vegetative phase and continue through the season to heading. Leaf blast will
usually appear in the high areas of the field where the flood has been lost or is
shallow. Areas of heavy nitrogen fertilization and edges of the fields are also
potential sites of infection. If leaf blast is in the field or has been reported in the
same general area, and if the variety is susceptible, fungicidal applications are
advisable to reduce rotten neck blast development and spread.
The pathogen overwinters as mycelium and spores on infected straw and
seed. Spores are produced from specialized mycelium called conidiophores and
become windborne at night on dew or rain. The spores are carried by air
currents and land on healthy rice plants. The spores germinate under high
humidity and dew conditions and infect the plant. Generally lesions will appear
four to seven days later, and additional spores are produced. Plants of all ages
are susceptible. Medium grain varieties are more susceptible to blast, especially
during the leaf phase, than the long grain varieties.
Environmental conditions that favor disease development are long dew
periods, high relative humidity, and warm days with cool nights. Agronomic
practices that favor disease development include excessive nitrogen levels, late
planting and dry soil (loss of flood). Several physiologic races of P. grisea exist,
and disease development varies, depending on variety-race interactions.
The disease can be reduced by planting resistant varieties, maintaining a
4- to 6-inch flood, proper nitrogen fertilizer, avoiding late planting, and by
applying a proper fungicide.
Brown Spot
Brown spot, caused by the fungus Cochiobolus miyabeanus, is another
prevalent rice disease in the south. When C. miyabeanus attacks the plants at
emergence, the resulting seedling blight causes sparse or inadequate stands and
weakened plants. Leaf spots are present on young rice, but the disease is more
prevalent as the plants approach maturity and the leaves begin to senesce.
Yield losses from leaf infection or leaf spots are probably not serious. When the
fungus attacks the panicle, including the grain, economic losses occur. Heavy
leaf spotting indicates an unfavorable growth factor, usually a soil-related
problem.
The pathogen also attacks the coleoptiles, leaves, leaf sheath, and
branches of the panicle, glumes, and grains. The fungus causes brown, circular
to oval spots on the coleoptile leaves of the seedlings. It may cause seedling
blight.
Leaf spots are found throughout the season. On young leaves, the spots
are smaller than those on older leaves. The spots may vary in size and shape
from minute dark spots to large oval and circular spots. The smaller spots are
dark brown to reddish-brown. The larger spots have a dark brown margin and a
light, reddish-brown or gray center. The spots on the leaf sheath and hulls are
similar to those on the leaves.
The fungus attacks the glumes and causes a general black discoloration.
It also attacks the immature florets, resulting in no grain development or kernels
that are lightweight and chalky.
Brown spot is an indicator of unfavorable growth conditions including
insufficient nitrogen, inability of the plants to use nitrogen because of rice water
weevil injury, root rot, or other unfavorable soil conditions. As the plants
approach maturity, brown spot becomes more prevalent, and the spots are larger
on senescing leaves.
Maintaining good growing conditions for rice by proper fertilization, crop
rotation, land leveling, proper soil preparation, and water management can
reduce damage from brown spot. Seed protectant fungicides reduce the severity
of seedling blight caused by this seedborne fungus. Some varieties are less
susceptible than others.
Crown Rot
Crown rot is suspected to be caused by a bacterial infection (possibly
Erwinia chrysanthemi). It is a minor disease usually associated with a specific
variety. Symptoms first appear during tillering. The crown area is decayed, softrotting, becoming black or dark brown with discolored streaks extending into the
lower internodes of culms. There is a putrid odor characteristic of bacterial soft
rots, and tillers start dying one at a time. The roots also die and turn black.
Adventitious roots are produced at the node above the crown area. A similar
discoloration of the crown can be caused by misapplied herbicides. Control
practices are not available.
Crown Sheath Rot
The fungus Gaeumannomyces graminis var graminis causes crown sheath
rot. Other names for this disease include brown sheath rot, Arkansas foot rot,
and black sheath rot. It has been considered a minor disease of rice, but
recent reports from Texas suggest severe damage can occur. The pathogen kills
lower leaves, reduces photosynthetic activity, causes incomplete grain filling, and
plants can lodge. Symptoms usually appear late in the season after heading.
Sheaths on the lower part of the rice plant are discolored brown to black.
Reddish-brown mycelial mats are found on the inside of infected sheaths. Dark
perithecia are produced within the outside surface of the sheath. Perithecia are
embedded in the sheath tissues with beaks protruding through the epidermis.
This disease can easily be confused with stem rot. The fungus survives as
perithecia and mycelia in plant residues. Ascospores are windborne in moist
conditions. The fungus has been reported to be seedborne. Management
practices have not been worked out for this disease.
Downy Mildew
The fungus Sclerophthora macrospora causes downy mildew. In early
growth stages, infected seedlings are dwarfed and twisted with chlorotic, yellow
to whitish spots. Symptoms are more severe on the head. Because of failure to
emerge, panicles are distorted, causing irregular, twisted and spiral heads that
remain green longer than normal. No management measures are
recommended.
False Smut
False smut is caused by the fungus Ustilaginoidea virens and is a minor
disease of rice grown in the southern region. The disease is characterized by
large orange to brown-green fruiting structures on one or more grains of the
mature panicle. When the orange covering ruptures, a mass of greenish-black
spores is exposed. The grain is replaced by one or more sclerotia. All varieties
appear to have a high level of resistance, and disease management measures
are not required.
Grain Spotting and Pecky Rice
Many fungi infect developing grain and cause spots and discoloration on
the hulls or kernels. Damage by the rice stink bug, Oebalus pugnax F., also
causes discoloration of the kernel. Kernels discolored by fungal infections or
insect damage are commonly called pecky rice. This complex disorder
involves many fungi, the white-tip nematode, and insect damage. High winds
at the early heading stage may cause similar symptoms. Proper insect control
and disease management will reduce this problem.
Kernel Smut
This fungal disease is caused by Tilletia barclayana. Symptoms are
observed at or shortly before maturity. A black mass of smut spores replaces all
or part of the endosperm of the grain. The disease is easily observed in the
morning when dew is absorbed by the smut spores. The black spore mass
expands and pushes out of the hull. When this spore mass dries, it is powdery
and comes off easily with fingers. Rain washes the black spores over adjacent
parts of the panicle. Affected grains are a lighter, slightly grayish color compared
with normal grain.
Usually only a few florets may be affected in a panicle, but fields have
been observed with 20 percent to 40 percent of the florets affected on 10 percent
or more of the panicles in a field. Smutted grains produce kernels with black
streaks or dark areas. Milled rice has a dull or grayish appearance when
smutted grains are present in the sample. Because fewer kernels break when
parboiled rice is milled, kernel smut can be a severe problem in processed rice.
Growers are docked in price for grain with a high incidence of smut. This
disease is usually minor, but it can become epidemic in local areas. Some
varieties are more susceptible and should be avoided where smut is a problem.
Spores of the fungus are carried on infected seeds and overwinter in the soil of
infected fields. The pathogen attacks immature, developing grain and is more
severe when rains are frequent during flowering. Specific management
measures are not available.
Leaf Scald
This disease, caused by Gerlachia oryzae, is common and sometimes
severe in Central and South America. It is present in the southern rice area of
the United States and in Louisiana annually. It affects leaves, panicles, and
seedlings. The pathogen is seedborne and survives between crops on infected
seeds. The disease usually occurs on maturing leaves. Lesions start on leaf tips
or the edges of leaf blades. The lesions have a chevron pattern of light (tan) and
darker reddish-brown areas. The leading edge of the lesion usually is yellow to
gold. Fields look yellow or gold. Lesions from the edges of leaf blades have an
indistinct, mottled pattern. Affected leaves dry and turn straw-colored. Panicle
infestations cause a uniform light to dark, reddish-brown discoloration of entire
florets or hulls of developing grain. The disease can cause sterility or abortion of
developing kernels. Management measures are not recommended, but foliar
fungicides used to manage other diseases have activity against this disease.
Leaf Smut
Leaf smut, caused by the fungus Entyloma oryzae, is a widely distributed,
but somewhat minor, disease of rice. The fungus produces slightly raised, black
spots (sori) on both sides of the leaves and on sheaths and stalks. The
blackened spots are about 0.5 - 5.0 mm long and 0.5 - 1.5 mm wide. Many spots
can be found on the same leaf, but they remain distinct from each other. Heavily
infected leaves turn yellow, and leaf tips die and turn gray. The fungus is spread
by airborne spores and overwinters on diseased leaf debris in soil. This disease
occurs late in the growing season and causes little or no loss. Control measures
are not recommended.
Narrow Brown Leaf Spot
Narrow brown leaf spot, caused by the fungus Cercospora janseana,
varies in severity from year to year and is more severe as rice plants approach
maturity. Leaf spotting may become very severe on the more susceptible
varieties causing severe leaf necrosis. Some premature ripening, yield reduction
and lodging occur.
Symptoms include short, linear, brown lesions most commonly found on
leaf blades. Symptoms also occur on leaf sheaths, pedicels and glumes. Leaf
lesions are 2 - 10 mm long and about 1 mm wide, tend to be narrower, shorter
and darker brown on resistant varieties and wider and lighter brown with gray
necrotic centers on susceptible varieties. On upper leaf sheaths, symptoms are
similar to those found on the leaf. On lower sheaths, the symptom is similar to a
“net blotch” or Cercospora sheath spot in which cell walls are brown and
intracellular areas are tan to yellow.
The primary factors affecting disease development are (1) susceptibility of
varieties to one or more prevalent pathogenic races, (2) prevalence of
pathogenic races on leading varieties and (3) growth stage. Although rice plants
are susceptible at all stages of growth, the plants are more susceptible from
panicle emergence to maturity.
Plant breeders have found differences in susceptibility among rice
varieties, but resistance is an unreliable control method because new races
develop readily. Some fungicides used to reduce other diseases also may have
activity against narrow brown leaf spot. Low nitrogen levels favor development of
the disease.
Root Knot
Species of the nematode Meloidogyne cause root knot. Symptoms include
enlargement of the roots and the formation of galls or knots. The swollen female
nematode is in the center of this tissue. Plants are dwarfed, yellow and lack
vigor. The disease is rare and yield losses low. The nematode becomes inactive
after prolonged flooding.
Root Rot
Root rots are caused by several fungi including Pythium spinosum, P.
dissotocum, other Pythium spp., and several other fungi. The rice plant is
predisposed to this disorder by a combination of factors including
physiological disorders, insect feeding, extreme environmental conditions and
various other pathogens.
Symptoms can be noted as early as emergence. Roots show brown to
black discoloration and necrosis. As the roots decay, nutrient absorption is
disrupted, the leaves turn yellow and the plants lack vigor. With heavy root
infections, plants lack support from the roots and lodge, causing harvest
problems. Often plants with root rot show severe brown leaf spot infection. The
disease is referred to as feeder root necrosis when the small fine roots and root
hairs are destroyed. When this happens, no lodging occurs and symptom
development is not as apparent on the upper plants.
Fertilizer usually reduces the aboveground symptoms although actual
nutrient use is impaired. Rice water weevil control greatly reduces root rots.
Draining fields stimulates root growth but can cause problems with blast, weeds,
or efficiency of nutrient use.
Seedling Blight
Seedling blight, or damping off, is a disease complex caused by several
seedborne and soilborne fungi including species of Cochiobolus, Curvularia,
Sarocladium, Fusarium, Rhizoctonia, and Sclerotium. Typically, the rice
seedlings are weakened or killed by the fungi. Environmental conditions are
important in disease development. Cold, wet weather is the most detrimental.
Seedling blight causes stands of rice to be spotty, irregular and thin. Fungi
enter the young seedlings and either kill or injure them. Blighted seedlings that
emerge from the soil die soon after emergence. Those that survive generally
lack vigor, are yellow or pale green and do not compete well with healthy
seedlings.
Severity and incidence of seedling blight depend on three factors: (1)
percentage of the seed infested by seedborne fungi, (2) soil temperature and
(3) soil moisture content. Seedling blight is more severe on rice that has been
seeded early when the soil is usually cold and damp. The disadvantages of early
seeding can be partially overcome by seeding at a shallow depth. Conditions
that tend to delay seedling emergence favor seedling blight. Treating the seed
with fungicides can reduce some blight fungi that affect rice seedlings at the time
of germination.
Seeds that carry blight fungi frequently have spotted or discolored hulls,
but seed can be infected and still appear to be clean. Cochiobolus miyabeanus,
one of the chief causes of seedling blight, is seedborne. A seedling attacked by
this fungus has dark areas on the basal parts of the first leaf.
If rice seed is sown early in the season, treating the seed is likely to mean
the difference between getting a satisfactory stand and having to plant a second
time. Little benefit is received from treating rice seed to be sown late in the
season, unless unfavorable weather prevails.
The soilborne seedling blight fungus, Sclerotium rolfsii, kills or severely
injures large numbers of rice seedlings after they emerge when the weather at
emergence is humid and warm. A cottony white mold develops on the lower
parts of affected plants. This type of blight can be checked by flooding the land
immediately.
Treatment of the seed with a fungicide is recommended to improve or
insure stands. Proper cultural methods for rice production, such as proper
planting date or shallow seeding of early-planted rice will reduce the damage
from seedling blight fungi.
Water- and soil-borne fungi in the genus Pythium attack and kill seedlings
from germination to about the three-leaf stage of growth. Infected roots are
discolored brown or black, and the shoot suddenly dies and turns straw-colored.
This disease is most common in waterseeded rice, and the injury is often
more visible after the field is drained. It may also occur in drill-seeded rice during
prolonged wet, rainy periods.
Seed treatment, planting when temperatures favor rapid growth of
seedlings, and draining the field are the best management measures for seedling
disease control.
Sheath Blight
Sheath blight has been the most economically significant disease in
Louisiana since the early 1970’s. The disease is caused by Rhizoctonia solani, a
fungal pathogen of both rice and soybeans. On soybeans, it causes the
aerial blight disease.
Several factors have contributed to the development of sheath blight from
minor to major disease status. They include the increased acreage planted to
susceptible long grain varieties, the increase in the acreage of rice grown in
rotation with soybeans, the increased use of broadcast seeding and the higher
rates of nitrogen fertilizers used with the modern commercial rice varieties. The
disease is favored by dense stands with a heavily developed canopy, high
temperature and high humidity.
Sheath blight is characterized by large oval spots on the leaf sheaths and
irregular spots on leaf blades. Infections usually begin during the late tillering joint elongation stages of growth. The fungus survives between crops as
structures called sclerotia or as hyphae in plant debris. Sclerotia or plant
debris floating on the surface of irrigation water serves as sources of inoculum
that attack and infect lower sheaths of rice plants at the waterline. Lesions about
0.5 - 1 cm in width and 1 - 3 cm in length are formed a little above the waterline
on infected culms. Fungus mycelium grows up the leaf sheath, forms infection
structures, infects, and causes new lesions. The infection can spread to leaf
blades. The lower leaf sheaths and blades are affected during the jointing
stages of growth. After the panicle emerges from the boot, the disease
progresses rapidly to the flag leaf on susceptible varieties. With very susceptible
varieties, the fungus will spread into the culm from early sheath infections.
Infected culms are weakened, and the tillers may lodge or collapse.
The fungus can spread in the field by growing from tiller to tiller on an
infected plant or across the surface of the water to adjacent plants. The fungus
also grows across touching plant parts, for example from leaf to leaf, causing
infections on nearby plants. Infected plants are us ually found in a circular pattern
in the field because the fungus does not produce spores and must grow from
plant to plant.
The lesions have grayish-white or light green centers with a brown or
reddish-brown margin. As lesions coalesce on the sheath, the blades turn
yellow-orange and eventually die. As areas in the field with dead tillers and
plants increase, they may coalesce with other affected areas to cause large
areas of lodged, dead and dying plants. Damage is usually most common where
wind-blown, floating debris accumulates in the corners of cuts when seedbeds
are prepared in the water.
Sheath blight also affects many grasses and weeds other than rice causing
similar symptoms. Sclerotia that survive between crops are formed on the
surface of lesions on these weed grasses, as well as on rice and soybeans. The
sclerotia are tightly woven masses of fungal mycelium covered by an impervious,
hydrophobic coating secreted by the fungus.
Integrating several management practices can reduce disease severity.
Dense stands and excessive use of fertilizer both tend to increase the damage
caused by this disease. Broadcast seeding tends to increase stand and canopy
density. Rotation with soybeans or continuous rice increases the amount of
inoculum in field soils. Fallow periods, with disking to control growth of grass
weeds, will reduce inoculum in the soil. The pathogen also is known to infect
sorghum, corn and sugarcane when environmental conditions are favorable for
disease development.
Medium grain rice varieties are more resistant to sheath blight than most of
the long grain varieties. Several recently released long grain varieties are more
resistant to sheath blight than the older long grain varieties. Fungicides are
available for reducing sheath blight.
Sheath Rot
This disease is caused by the fungal pathogen Sarocladium oryzae.
Symptoms are most severe on the uppermost leaf sheaths that enclose the
young panicle during the boot stage. Lesions are oblong or irregular oval spots
with gray or light brown centers and a dark reddish-brown, diffuse margin. The
lesions may form an irregular target pattern. On U.S. rice varieties, the lesion is
usually expressed as a reddish-brown discoloration of the flag leaf sheath. Early
or severe infections affect the panicle so that it only partially emerges. The
unemerged portion of the panicle rots, turning florets red-brown to dark brown.
Grains from damaged panicles are discolored reddish-brown to dark brown and
may not fill. A powdery white growth consisting of spores and hyphae of the
pathogen may be observed on the inside of affected sheaths. Insect or mite
damage to the boot or leaf sheaths increases the damage from this disease.
This disease affects most rice varieties. The disease is usually minor,
affecting scattered tillers in a field. Occasionally, larger areas of a field may have
significant damage. Control measures are not recommended. Fungicidal sprays
used in a general disease management program reduce damage, but recent
studies show that several bacterial pathogens commonly cause similar sheath rot
symptoms on rice. Fungicides would have little to no effect on these pathogens.
Sheath Spot
The fungus Rhizoctonia oryzae causes this disease. The disease
resembles sheath blight, but is usually less severe. The lesions produced by R.
oryzae are found on sheaths midway up the tiller or on leaf blades. Lesions are
oval, 0.5 - 2 cm long and 0.5 - 1 cm wide. The center is pale green, cream or
white with a broad, dark reddish-brown margin. Lesions are separated on the
sheath or blade and do not form the large, continuous lesions often found with
sheath blight. The pathogen attacks and weakens the culm under the sheath
lesion on very susceptible varieties. The weakened culm lodges or breaks over
at the point where it was infected. Lodging caused by sheath spot usually occurs
midway up the culm.
This disease is usually minor on southern rice. Some fungicides used to
manage sheath blight also reduce sheath spot.
Stackburn
This disease was first observed on rice growing in Louisiana and Texas.
Stackburn or Alternaria leaf spot is caused by the fungal pathogen Alternaria
padwickii. It is now common on rice around the world.
The disease is present in all rice fields in Louisiana. Only occasional spots
are observed, but the disease may be more severe in restricted areas of a field.
The spots are typically large (0.5 - 1 cm in diameter), oval or circular, with a dark
brown margin or ring around the spot. The center of the spot is initially tan and
eventually becomes white or nearly white. Mature spots have small dark or black
dots in the center. These are sclerotia of the fungus. Grain or seeds affected by
the disease have tan to white spots with a wide, dark brown border. The disease
causes discoloration of kernels, or the kernels stop development and grains are
shriveled.
No specific control recommendations are available, but seed-protectant
fungicides will help reduce the seedling blight caused by this pathogen and will
reduce the number of spores available to cause leaf infections.
Stem Rot
Stem rot caused by the fungus Sclerotium oryzae is an important disease
in Louisiana. Often, losses are not detected until late in the season when it is
too late to initiate control practices. Stem rot causes severe lodging, which
reduces combine efficiency, increases seed sterility, and reduces grain filling.
The first symptoms are irregular black angular lesions on leaf sheaths at or
near the water line on plants at tillering or later stages of growth. At later stages
of disease development, the outer sheath may die, and the fungus penetrates to
the inner sheaths and culm. These become discolored and have black or dark
brown lesions. The dark brown or black streaks have raised areas of dark fungal
mycelium on the surface and gray mycelium inside the culm and rotted tissues.
At maturity, the softened culm breaks, infected plants lodge and many small,
round, black sclerotia develop in the dead tissues.
The pathogen overwinters as sclerotia in the top 2 - 4 inches of soil and on
plant debris. During water-working and establishment of early floods, the
hydrophobic sclerotia float on the surface of the water and often accumulate
along the edge of the field and on levees due to wind.
After a permanent flood is established, the sclerotia float to the surface,
contact the plant, germinate and infect the tissues near the waterline. The
fungus then penetrates the inner sheaths and culm, often killing the tissues. The
fungus continues to develop, forming many sclerotia in the stubble after harvest.
Most commercial varieties of rice are not highly resistant to stem rot. The
disease is favored by high nitrogen levels. Early maturing varieties are usually
less affected by stem rot. In addition, applications of potassium fertilizer reduce
disease severity in soils where potassium is deficient. Stem rot is more serious
in fields that have been in continuous rice production for several years.
Suggested management measures include using early maturing varieties,
avoiding very susceptible varieties, and burning stubble. Cultivation after harvest
can destroy sclerotia. Using crop rotation when possible, applying potassium
fertilizer, avoiding excessive nitrogen rates, and applying foliar fungicides also
aid in control. Several cultural practices may reduce stem rot. These include
fluctuating the water level in the field so stagnant water does not remain at the
same level on the lower leaf sheaths, and draining water from the field at the
tillering and early jointing stages of growth, while keeping the soil saturated.
However, caution is advised as these practices may lead to the development of
leaf blast and other problems.
Water-Mold and Seed-Rot
With the extensive use of the waterseeding method of planting rice, it has
become more difficult to obtain uniform stands of sufficient density to obtain
maximum yields. The most important biological factor contributing to this
situation is the water-mold or seed-rot disease caused primarily by fungi in the
genera Achlya and Pythium. Recently, certain Fusarium spp. also have been
found associated with molded seeds. The disease is caused by a complex of
these fungi infecting seeds. The severity of this disease is more pronounced
when water temperatures are low or unusually high. Low water temperatures
slow the germination and growth of rice seedlings but do not affect growth of
these pathogens .
In addition to the direct cost of the lost seeds and the cost of replanting,
watermold also causes indirect losses caused by the reduced competitiveness of
rice with weeds in sparse or irregular stands. Also, replanting or overseeding the
field causes the rice to mature late when conditions are less favorable for high
yields because of unfavorable weather and high disease pressure.
Water mold can be observed through clear water as a ball of fungal
strands surrounding seeds on the soil surface. After the seeding flood is
removed, seeds on the soil surface are typically surrounded by a mass of fungal
strands radiating out over the soil surface from the affected seeds. The result is
a circular copper-brown or dark green spot about the size of a dime with a rotted
seed in the center. The color is caused by bacteria and green algae, which are
mixed with the fungal hyphae.
Achlya spp. normally attacks the endosperm of germinating seeds,
destroying the food source for the growing embryo and eventually attacking the
embryo. Pythium spp. usually attacks the developing embryo directly. When the
seed is affected by the disease, the endosperm becomes liquefied and oozes o ut
as a white, thick liquid when the seed is mashed. The embryo initially turns
yellow-brown and finally dark brown. If affected seeds germinate, the seedling
shoot and root are attacked and the seedling is stunted. When infection by
Pythium spp. takes place after the seedling is established, the plant is stunted,
turns yellow and grows poorly. If the weather is favorable for plant growth,
seedlings often outgrow the disease and are not severely damaged.
The disease is less severe when rice is water-seeded when weather
conditions favor seedling growth. High and low temperatures averaging above
65° F favor seedling growth, and water mold is less severe. Seeds should be
vigorous and have a high germination percentage. Seed with poor vigor will be
damaged by water-mold fungi when water-seeded.
Treat seed with a recommended fungicide at the proper rate to reduce
water molds and seed diseases. Most rice seed is treated by the seedsman and
is available to the grower already treated. Seed-protectant fungicides differ in
their effectiveness.
White Tip
This disease is caused by the nematode Aphelenchoides besseyi.
Characteristic symptoms which appear after tillering include the yellowing of
leaf tips, white areas in portions of the leaf blade, stunting of affected plants,
twisting or distortion of the flag leaf, and distortion and discoloration of
panicles and florets. Leaf tips change from green to yellow and eventually
white. The tip withers above the white area, becoming brown or tan and tattered
or twisted. Resistant varieties may show few symptoms and still have yield loss.
The nematode infects the developing grain and is seedborne.
This disease is considered minor. Fumigation of seeds in storage will
reduce the nematode population. No other specific control measures are
recommended.
Chemical Disease Control Guidelines:
Moncut 70 DF (flutolanil) Apply 0.5 - 0.71 lb. a.i./A by air in 5 - 10 gpa to
control sheath blight. Apply at first internode elongation, and follow with a
second application at the same rate 10 - 14 days later. Use the higher
rate where disease pressure is expected to be heavy. In fields where
close scouting is practiced to detect and monitor sheath blight, apply 0.5 1.0 lb. a.i./A when 5 - 10% of the tillers of a susceptible variety or 10 - 15%
of the tillers of a moderately susceptible variety have blight lesions.
Continue scouting and reapply if disease begins to move up the rice stem
again.
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Do not apply more than 1.43 lb. a.i./A per given year.
Do not apply later than 30 days prior to harvest, or beyond 75%
heading development stage, whichever comes first.
This pesticide is toxic to shrimp. Do not apply within 3 miles of any
estuarine/marine waterways or watershed.
Flooded fields may be used for aquaculture of crayfish only
following rice harvest.
Do not enter treated fields for 12 hours after application
Quadris 2F (azoxystrobin) Apply 0.15 - 0.20 lb. a.i./A by ground, air (5 10 gpa), or chemigation. For panicle blast on rice not grown in rotation
with another crop, apply no more than 2 sequential applications of Quadris
over multiple years before alternating to a fungicide with a different mode
of action. For stem/sheath diseases including stem rot, black sheath rot,
and sheath spot, apply when disease is less than 4 inches above water
line usually between panicle differentiation (PD) +5 days to PD +10 days
or at initial sign of disease. Under heavy disease pressure, a second
application may be applied. For foliar and panicle diseases, apply as a
preventative treatment prior to disease development. For panicle blast, an
application should be made at mid-boot to boot-split but prior to full head
emergence. A second application should be made when panicles are 60 90% emerged from the boot (7 - 14 days later).
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Do not treat rice fields used for aquaculture of fish and crustaceans .
Do not apply when weather conditions favor drift. Use care when
making applications near non-target aquatic habitats.
Do not apply more than 0.6 lb. ai/A per season.
Do not apply within 28 days of harvest.
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Do not allow release of irrigation or floodwater for at least 14 days
after last application.
Do not apply more than 2 applications of Quadris or other
strobiluron fungicide per season.
Do not enter treated fields for 4 hours after application.
Tilt (propiconazole) When applied by air in 5 - 10 gpa, Tilt controls sheath
blight, brown leaf spot, narrow brown leaf spot, brown blotch, leaf smut,
sheath spot, and black sheath rot. It can suppress stem rot. Apply on
either of the following schedules:
A. 6 fl. oz./A at first internode elongation (up to 2-inch panicle) and
repeat at swollen boot. Make the second application 10-14
days after the first application but before the boot splits and
head emerges. Tilt provides best control of sheath blight when
the first application is applied at disease appearance in the field.
The first application is recommended when 5% or fewer of the
tillers are infected.
B. 10 fl. oz./A at first internode elongation (up to 2-inch panicle).
The 10 oz. rate is recommended if greater than 10% of the
tillers are infected with sheath blight. If disease reappears, use
another registered fungicide for the second application.
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Do not apply to stubble or ratoon crop rice.
Do not use in rice fields where commercial farming of crayfish will
be practiced.
Do not drain water from treated rice fields into ponds used for
commercial catfish farming.
Do not use water drained from treated fields to irrigate other crops.
Unless soil-injected or soil-incorporated, do not enter treated fields
for 24 hours after application.
Apron XL LS (mefenoxam) Apply as a seed treatment at 0.0425 - .085 fl.
oz./cwt of seed to control Pythium seed rot and damping off. Apron can
be used in conjunction with Vitavax CT. Follow label directions closely
when mixing seed treatments. Unless soil-injected or soil-incorporated, do
not enter treated fields for 48 hours after application.
Vitavax CT (carboxin) Apply as a seed treatment at 9 - 12 fl. oz./cwt of
seed to control Rhizoctonia solani and Helminthosporium oryzae. Vitavax
CT is toxic to fish. Do not apply directly to water.
PHYSIOLOGICAL DISORDERS
Cold Injury
Cold weather affects rice development most at the seedling or reproductive
stages of growth. Seedling damage is expressed as a general yellowing of the
plants or as yellow or white bands across the leaves where a combination of
wind and low temperature damaged the plants at the soil line. Cold weather
(less than 60° F) present during the reproductive stages causes panicle
blanking or blighting. Individual florets or the whole panicle may be white when
emerging. To eliminate this problem, adjust planting date to avoid low
temperatures.
Panicle Blight
Panicle blight or grain blight was recently identified as being caused by the
bacterium Burkholderia glumae. The bacterium is seedborne and can cause a
seedling blight that can thin stands significantly. The bacterial population
appears to follow the growing plant as an epiphytic population on the foliage.
This population infects the grain at flowering and causes grain abortion and grain
rotting soon after pollination. Yield loss estimates vary from a trace to 50 percent
yield and quality losses.
Initial symptoms of grain infection appear as a gray discoloration of the
glumes. Infected grains can be unevenly distributed on the panicle. In severe
infections, all of the seed can be damaged. Diagnosis is difficult because of
other causes of seed infection and sterility producing similar symptoms and
masking panicle blight symptoms after lesion maturity. A key diagnostic
characteristic is the stem staying green up to the seed.
High temperatures favor the disease. It usually develops in a circular
pattern in the field with severely affected plants in the center and less affected
plants around the edge. Infected heads can be confused with straighthead
because of their upright stature. No parrot beaks are present. Some varieties
are less susceptible than others. Chemical control measures are being
developed. Seed treatments have shown some activity in reducing seedborne
pathogen populations and subsequent head severity.
Salinity
Soil alkalinity, or salinity, and water salinity injure rice and are
characterized by areas of stunted, chlorotic plants in the field. Under severe
conditions, leaves turn from yellow to white, and plants die. Affected areas
usually have dead or dying plants in the center or on high spots, with stunted
yellow or white plants surrounding that area and green, less affected plants in
lower areas. Salt deposits may be seen on the edges of leaves, on clods of soil
and other high areas of the field. Flushing with water low in salt reduces
damage.
Straighthead
Straighthead is a physiological disorder associated with sandy soils, fields
with arsenic residues or fields having large amounts of plant residue incorporated
into the soil before flooding. Panicles are upright at maturity because the grain
does not fill or panicles do not emerge from the flag leaf sheath. Hulls (palea and
lemma) may be distorted and discolored, with portions missing or reduced in
size. Distorted florets with a hook on the end are called “parrot beak” and are
typical of straighthead. Plants are darker green or blue-green and often produce
new shoots and adventitious roots from the lower nodes. These symptoms can
be mimicked by herbicide damage. Manage by using resistant varieties and
draining at the first internode elongating stage of growth to dry the soil until it
cracks. Do not plant susceptible varieties under conditions favorable for
straighthead development, which include very sandy soils, soils with high levels
of undecomposed plant residue or fields with a history of arsenical herbicide
(such as MSMA) applications.
WEEDS
Introduction
Weeds compete with rice for water, nutrients, space and light. Direct
losses from weed competition are measurable and can be great. Indirect losses
such as increased costs of harvesting and drying, reduced quality and dockage
at the mill, and reduced harvest efficiency are not readily measured but can
reduce profits. Numerous grasses, broadleaf weeds and sedges can be
economically damaging in rice. Weeds can grow and thrive in aquatic or
semiaquatic environments common to rice culture. Barnyardgrass, broadleaf
signalgrass, red rice, hemp sesbania, alligatorweed, dayflower, ducksalad,
redstem, jointvetch, and annual and perennial sedges are among the most
common weeds. Althoug h weeds vary in their ability to compete with rice, most
fields contain a complex of weeds which will reduce yield and quality if an
appropriate weed management strategy is not implemented.
Rice weed control is best accomplished by using a combination of cultural,
mechanical and chemical control practices. Relying on a single control practice
seldom provides adequate weed control. A thorough knowledge of the weeds
present in each field is critical in developing appropriate management strategies.
Cultural Control
Purchasing seed rice that is weed free is an important first step in
preventing weeds from becoming established, especially in the case of red rice.
Red rice has been spread largely by planting commercial seed that is
contaminated. Red rice is a wild rice that is similar to commercial rice. Besides
reducing commercial rice yields, the red pericarp of this noxious rice can
contaminate milled rice. Additional milling can help remove the red discoloration
but often will lead to reduced head rice yields through breakage of kernels.
Cooking attributes of rice can be altered if significant amounts of red rice are
present in milled rice. Newer selective herbicide management strategies for red
rice will be discussed later in the weed management section.
Presence of red rice dictates production systems and weed control options
and decreases flexibility. Rotating rice with other crops can reduce future weed
problems. Successful rotations with soybeans primarily and to a lesser extent
with corn, sorghum, soybeans or cotton have reduced levels of red rice in later
rice crops.
Proper water management is a key component in controlling weeds.
Several different water management schemes have evolved. Permanent flood
and pinpoint flood cultures were developed in water-seeded rice to reduce weed
problems. These practices attempt to maintain a saturated seedbed. Saturated
seedbeds prevent weed seeds from germinating because of the absence of
oxygen.
Establishi ng a good stand of rice and providing an environment that
promotes rapid growth also help to minimize weed interference. Optimum plant
populations and adequate fertility, insect, disease and water management
contribute to the ability of rice plants to compete with weeds.
Management of weeds is critical for optimum rice production in both water
and dry-seeded systems. Although herbicide options and management
strategies differ under these systems, managing herbicides and water in a timely
manner is critical.
Water-seeded rice
Weed populations shift from terrestrial weeds in dry-seeded systems to
aquatic weeds in water-seeded systems. Red stem, ducksalad, alligatorweed
and rushes are prevalent in water-seeded systems. Grasses such as
barnyardgrass and broadleaf signalgrass as well as some warm-season
perennial grasses (e.g., water bermuda) in some areas can be a problem also.
In water-seeded systems, Bolero or Ordram are applied before seeding to
suppress aquatic weeds and grasses. After seedling establishment, propanil,
Arrosolo and Facet are used to control grasses and broadleaf weeds. These
herbicides are often supplemented with Basagran to control ducksalad and red
stem. The field is generally drained briefly to expose weeds to herbicides. When
doing so, it is important that the soil remain wet in fields where red rice is
present. Allowing the soil to dry can result in reinfestation by red rice.
Granular Ordram also controls grasses and can be applied directly in the
floodwater. Londax has become a standard for use in water-seeded rice to
control ducksalad and other difficult-to-control aquatic weeds. Applying Londax
at the appropriate timing is critical to control. Londax is applied into the floodwater before aquatic weeds have surfaced, and a stationary flood must be
maintained for seven days for acceptable control. Some dealers offer fertilizer
materials impregnated with Londax, an effective application that reduces cost.
Several herbicides are available for post-flood weed control in both waterand dry-seeded systems. Facet, Blazer, Basagran, Grandstand, Londax and
2,4-D are registered for use. Selection of these herbicides should be based on
the spectrum of weeds and restrictions on use. For example, 2,4-D use is
prohibited where rice is grown in close proximity to cotton and other 2,4-Dsensitive crops. Although registered for use, apply Whip 360 only in salvage
situations when other herbicides have failed to control grass weeds. Excessive
rice injury can occur. Precautions on variety selection and cultural practices that
may contribute to injury should be considered before use.
Problem weed species
barnyardgrass - A warm-season vigorous grass reaching up to 5 feet,
barnyardgrass (Echinochloa crus-galli) has panicles that may vary from reddish
to dark purple. The seed heads contain crowded large seeds in spikelets, each
with a short, stiff awn. Leaf blades are flat, 3/8 to 5 /8 inch wide, smooth, and
without a ligule, a papery-like membrane at the collar of the plant where the leaf
blade contacts the stem. The stem is flat—not round.
red rice - Red rice is so closely related genetically to commercial rice that
anything that will control red rice will generally kill the crop. In fact, it’s the same
species—Oryza sativa. Red rice plants vary considerably. The tall-growing,
black-hulled, awned plant is easiest to recognize and is considered by many to
be a typical red rice plant. However, other strains have developed that have
straw-colored hulls, are awnless and are about the same height as desirable rice
varieties.
alligatorweed - Alligatorweed (Alternanthera philoxeroides) is an aquatic
perennial that forms dense floating mats. It has hollow stems, opposite leaves
with distinctive midribs and a single white flower head. The leaves are elliptically
shaped and 1 /4 to 3/4 inch wide.
hemp sesbania - Commonly called coffeebean or coffeeweed, hemp sesbania
(Sesbania exaltata) is a tall, blue -green, spindly weed growing up to 12-14 feet.
The plants have a yellow, pea-like flower. Seed pods are 4-8 inches long, curved
and often tipped with a 1/2 -inch-long beak. The leaves are opposite and may
feature as many as 70 leaflets with a smooth surface and somewhat hairy
surface below.
broadleaf signalgrass - A spreading summer annual, broadleaf signalgrass
(Brachiaria platyphylla) has short, wide leaf blades, ranging from 1 1/2 to 6 inches
long and 1/4 to 2 /3 inch wide. Leaf blades are typically hairless, except for hairs
that occur in the margins and the lower portion of young plants. It doesn’t have a
ligule, a papery-like membrane at the junction of the sheath and leaf blade.
ducksalad - An aquatic annual or perennial, ducksalad (Heteranthera limosa)
grows in open water either near water inlets or in openings in sparse stands.
The mature plant grows up to 6 inches tall. Leaf blades may either narrow to a
point or be duckbilled at the tip.
redstem - An erect, simple or freely branched annual, redstem (Ammannia
coccinea) grows to 11/2 tall, the branches ascending, or basal branches, when
present, spreading.
jointvetch - Two different species may infest rice fields: Indian jointvetch
(Aeschynomene indica) and northern jointvetch (Aeschynomene virginica). Both
are upright and usually bushy, growing up to 3-4 feet tall. Indian jointvetch differs
from northern jointvetch in that its fruit stalk and leaflets are shorter and its flower
smaller. Northern jointvetch plants have large stipules or bracts at the base of
the leaf stalk or petiole. Both have pea-like flowers and can be distinguished
from hemp sesbania because of a smaller size and more delicate appearance.
The alternating leaves have as many as 56 oblong leaflets with smooth edges.
Leaflets fold when touched.
dayflower - A crawling, spreading summer annual, dayflower (Commelina
communis) grow up to 2 feet. The plant may grow either upright or creeping with
numerous branches sprouting at the nodes and stems. Leaves have
conspicuous sheaths at the base, and flowers feature two upright blue petals and
one smaller white petal. The egg-shaped leaves are 1 /3 to 1/2 inch long and 1 /3 to
11/2 inches wide.
yellow nutsedge - Also called yellow nutgrass, yellow nutsedge (Cyperus
esculentus) is an aggressive plant that grows between 3 and 32 inc hes and has
adapted to water culture. Distinctive features include a yellow umbrella-like seed
head and smooth three-ranked leaves that gradually taper to a small point.
Fibrous roots grow from bulbs, rhizomes or tubers. Stems are triangular and
rarely b ranch from the tuber or basal bulb.
morningglories (Ipomoea sp.), annual, climbing vine reaching over 6 feet.
Introduced native of tropical America. Chordate and lobed-shaped leaves
depending upon species.
Texas weed - Although also referred to as Mexicanweed (Caperonia
castanifolia), Texasweed (Caperonia palustrus) is a different species. The
annual upright plant grows to about 2-3 feet tall with coarse male and female
flowers with unique three-capsuled fruit. Leaves are alternating and broad, with
serrated edges.
smartweeds (Polygonum sp.), erect, summer annual with some species reaching
6 feet. Leaf blades ovate-lanceolate to lanceolate . Stems with swollen nodes.
eclipta - A spindly growing annual weed, Eclipta (Eclipta prostrata) has simple
opposite leaves. Leaves measure 3 -5 inches long and are elliptical, lacking
stalks. Lower surfaces of leaves are hairy. Stems feel sand papery.
sprangletop - Three species of sprangletop may infest rice fields—Mexican
sprangletop (Leptochloa uninervia), bearded sprangletop (Leptochloa fasciculais)
and red sprangletop (Leptochloa filifomis). All three are tall with thin, flat leaf
blades, running 1/4 to 1 /3 inch wide and up to 12 inches long. Sprangletop has a
ligule, a papery-like membrane at the collar of the plant where the leaf blade
contacts the stem. All three have a large, open panicle when mature.
Dry-seeded production
In this system, four to six weeks may elapse between planting and
permanent flood establishment, and controlling weeds duri ng this period is critical
for maximizing yields. During this period barnyardgrass, broadleaf signalgrass,
sprangletop, morningglories, texasweed, eclipta, jointvetch, smartweeds and
hemp sesbania can become established. Timely herbicide applications made to
small weeds, flushes to activate herbicides, and establishment and maintenance
of a permanent flood as soon as possible will improve weed control.
The residual herbicides Prowl, Facet and Bolero can provide residual weed
control up to permanent flood establishment, and these herbicides have
proven valuable in dry-seeded production. They are especially beneficial when
delays in permanent flood establishment are anticipated or on clay soils where
cracking of soil promotes numerous weed flushes as well as difficulty in
establishing and maintaining a permanent flood. Although these herbicides do
not always provide complete control, when applied in a program with propanil or
Arrosolo, these herbicides generally provide adequate control up to permanent
flood establishment. These herbicides, and in particular Facet, are more
effective when fields are flushed or when adequate rainfall occurs for activation.
Propanil, Arrosolo and Facet are used routinely to control emerged weeds
before flood establishment. Propanil is a contact herbicide with no residual
activity. Arrosolo contains both propanil and molinate, and it provides contact
and limited residual weed control. Facet controls emerged weeds, but, unlike
propanil and Arrosolo, root absorption of Facet is important. Flushing or
adequate rainfall shortly after application of Facet is needed for activation
regardless of whether or not weeds have emerged. Combinations of contact
herbicides such as propanil and Arrosolo with the residual herbicides like Facet,
Bolero or Prowl are often more effective than single herbicide applications.
Weeds that are not under moisture stress and are actively growing are controlled
more easily than stressed weeds.
Grandstand, Londax, Basagran, Storm and Blazer can be applied preflood
in dryseeded systems. Propanil, Arrosolo and Facet are generally needed for
grass control, and these broadleaf herbicides are used to broaden the spectrum
of control. Grandstand controls morningglories, jointvetch and alligatorweed.
Londax and Basagran are used to control sedges and certain broadleaf and
aquatic weeds.
Herbicide programs should be developed based on the complex of weeds
present in each field. Scouting fields and accurately identifying weeds are
critical in formulating herbicide programs. For example, Facet provides excellent
control of barnyardgrass but does not control sprangletop. Relying on Facet
alone for weed control will result in sprangletop escapes which can compete
with rice. A n additional herbicide application will be needed to control sprangletop, and the delay in application caused by misidentification can make
sprangletop more difficult to control. Annual sedges can often be controlled
with propanil or Arrosolo, but these herbicides seldom control yellow nutsedge
adequately when applied alone; Basagran or Londax is generally needed.
In dry-seeded systems, pulling levees as soon as possible after planting
can improve weed control by allowing fields to be flushed and flooded in a timely
manner. Without levees, using water as a management tool is impossible. On
coarse-textured, silt loam soils, pulling levees is much easier than on finertextured, clay soils. Although rainfall shortly after planting is beneficial for
establishing a rice stand and reducing the need for flushing, excessive rainfall
can prevent levee construction on clay soils. Pulling levees as soon as the rice is
planted when the soil is still relatively dry can prevent or reduce problems in
preparing levees on wet soils.
Adjuvants and Spray Additives
Postemergence herbicide performance can be greatly influenced by
adjuvants. Grandstand, Londax, Basagran, Facet and the dry formulations of
propanil must be applied with a suitable adjuvant to control emerged weeds.
Gramoxone Extra and Harmony Extra applied as burndown treatments require
adjuvants. In contrast to these herbicides, adjuvants will not improve control with
emulsifiable propanil, Arrosolo or Whip 360. Bolero, Facet (preemergence or
delayed preemergence), Prowl or Ordram applied to the soil before weed
emergence does not require adjuvants. When a liquid propanil formulation or
Arrosolo is applied with Grandstand, Londax, Facet or Basagran, additives are
not needed. When Facet or dry formulations of propanil are mixed with these
predominantly broadleaf herbicides, however, an adjuvant should
be included.
Adjuvant cost is much lower than the cost of a herbicide application,
especially when several herbicides are applied as a mixture. Not using an
adjuvant or selecting a poor quality adjuvant can reduce weed control greatly.
Consult the herbicide label for recommendations of the type of adjuvant (crop oil
concentrate, nonionic surfactant, etc.) and the proper rate to use.
Reduced-tillage and stale seedbed
systems
Producing rice in stale seedbed, reduced-tillage or no-till systems requires
use of burndown herbicides applied before seeding in water-seeded systems
and before rice emergence in dry-seeded systems. Timing of application will
depend on the spectrum and size of weeds, anticipated planting date and label
restrictions. The key is to have a weed free seedbed when the rice emerges
(dryseeded rice) or when the flood is established in water-seeded systems. A
problem associated with no-till, waterseeded rice is poor water quality and low
oxygen resulting from decaying plant residue. Timely vegetation management
can minimize this situation. Roundup Ultra, Gramoxone Extra, 2,4-D and
Harmony Extra are registered for use in rice. Applying combinations of Roundup
Ultra with 2,4-D or Harmony Extra increases control of some broadleaf weed
species and may broaden the spectrum of control. Each of these has strengths
and weaknesses, and herbicide programs should be tailored to control the
existing weed spectrum. Gramoxone Extra has the advantage of rapid kill of
weeds and requires only a two -day period before the flood can be established for
seeding in water-seeded systems. This is an advantage in controlling red rice.
These herbicides also have restrictions on preplant intervals which can
potentially limit utility. For example, Harmony Extra cannot be applied within 45
days of planting. Additionally, various formulations of 2,4-D are available, and
labels vary on rates and preplant intervals. Applying Roundup and Gramoxone
Extra with residual herbicides such as Bolero, Prowl and Facet can improve
early-season weed control. Bolero can be applied in dry- and water-seeded
systems, and Prowl can be applied only as a delayed preemergence
application in dry-seeded systems. Facet can be applied preemergence or
delayed preemergence in dry-seeded systems. It is critical to establish a weedfree seedbed for the emerging rice in dry- and waterseeded systems. When
weeds are not controlled and rice has emerged, control can be difficult with inseason herbicides for most winter annual and perennial weeds. Also, summer
annual weeds that are not controlled before rice emergence will be older, larger
and often harder to control with propanil or other rice herbicides.
Weed Resistance
Some weeds have developed resistance to herbicides. In situations where
weeds are not controlled with labeled rates of herbicides applied under
environmental conditions which are favorable for herbicide activity, these weeds
may be resistant. Repeated use of propanil has resulted in development of
biotypes throughout the Mid-South that can no longer be controlled with propanil.
Aquatic weeds in California have developed resistance to Londax. Rotating
herbicides and crops, and applying tank mixtures consisting of herbicides with
different mechanisms of action, may prevent or delay development of resistance
in Louisiana. For example, mixtures of propanil with Facet, Bolero o r Prowl
include at least two different mechanisms of action and reduce selection
pressure. Rotating rice with soybeans or other crops will allow use of soil-applied
herbicides or postemergence grass herbicides which can control barnyardgrass
and red rice. These herbicides have mechanisms of action that differ from most
rice herbicides.
If weed resistance is suspected, contact your county agent so an
alternative herbicide program can be developed and resistance can be
monitored. In addition to developing potential weed resistance, repeated use of
a single herbicide will exploit the weakness of the herbicide and may shift the
weed spectrum to weeds that may be more difficult to control. This has been
especially true in continued use of Facet only, which has resulted in a shift
from barnyardgrass as the primary grass weed to sprangletop.
Red Rice Management
Because red rice and commercial rice are so closely related genetically,
herbicides that control red rice will generally kill commercial rice. Water
management alone can often effectively suppress red rice and reduce
competition. Red Rice is a growing problem throughout the three-state growing
region. However, this weed is a larger problem in south-central and southern
Louisiana. Predicting its spread is difficult. Presence of red rice mandates that
rice be produced in a water-seeded system, preferably the pinpoint production
system. Uniform, level seedbeds are critical for success. Presoaked seed is
preferred because it gives the commercial rice an additional advantage over the
red rice. Before flying on the rice seed, the field is tilled to muddy the water and
kill germinated red rice that would otherwise emerge through clear water. This
type of tillage can be difficult on cla y soils. Depending on environmental
conditions, the flood is removed and rice seedlings are allowed to peg into the
soil. An advantage of presoaked seed is that the flood can be removed sooner
than with dry rice. This can reduce the time seeds are exposed to wind and drift
within bays and can help lead to a more uniform stand. After rice seedlings have
anchored, the flood is brought up slowly until the permanent flood is established.
Maintenance of flooded soil conditions reduces emergence of red rice and other
weeds. Water management in this system is critical, and breakdowns in control
usually result from inadequate flood maintenance.
Although Bolero and Ordram suppress red rice, they do not provide
complete control. Using these herbicides in combination with water
management, however, can minimize interference from red rice. Rotating rice
with soybeans or other crops and controlling red rice with effective herbicides are
important in managing red rice.
Recently, Newpath (imazethapyr) selectivity has become a tool to use in
the management of red rice and annual grasses. Newpath can only be applied
to Clearfield (imidazolinone-tolerant) rice varieties that have been dry seeded or
drill planted.
Summary
Numerous herbicides and tank mixtures of herbicides are available for use
in rice, and, with the exception of red rice, adequate weed control can be
obtained when these herbicides are applied in a timely manner coupled with
appropriate water management. Early season weed interference can be very
detrimental and can reduce yields even though control practices are
implemented later. Failure to apply herbicides in a timely manner may result in
poor weed control and the need for repeat applications. These situations a llow
more early-season weed competition and generally less effective control.
Before using a herbicide, follow all directions and precautions. In addition
to being illegal, failure to follow the label can result in poor weed control,
excessive rice injury and environmental and safety hazards.
Chemical Weed Control Guidelines
Preplant Burndown
Roundup (glyphosate) Apply 0.5 - 1.5 lb. a.i./A to control actively growing
weeds. Apply at least 7 days before flood establishment in water-seeded
systems and prior to rice emergence in dry-seeded systems. Requires 7 to 21
days to kill most weeds. Applying with 2,4-D or Harmony Extra may broaden the
spectrum of control. Do not enter treated fields for 4 hours after application.
Gramoxone Extra (paraquat) Apply 0.5 - 1.5 lb. a.i./A to control emerged annual
weeds. May defoliate perennial weeds but will not kill them. Apply at least 2
days before flood establishment in water-seeded systems and prior to rice
emergence in dry seeded systems. Add surfactant at 0.25% - 0.5% on a volume
basis. Do not enter treated fields for 12 hours after application.
2,4-D (various trade names) Apply 0.5 - 1.0 lb. a.i./A to control emerged
broadleaf weeds. Apply at least 2 weeks before planting or flood establishment
depending upon the formulation. Add surfactant at 0.25% - 0.5% on a volume
basis. Do not enter treated fields for 12 hours after application.
Harmony Extra (thifensulfuron+tribenuron) Apply 0.015 - 0.023 lb. a.i./A for
emerged broadleaf weeds. Apply at least 45 days before planting. Add
surfactant at 0.25% on a volume basis. Do not enter treated fields for 12 hours
after application.
Roundup + Harmony Extra (glyphosate + thifensulfuron+tribenuron) Apply 0.5 1.5 + 0.015 - 0.023 lb. a.i./A for improved control of curly dock, cutleaf evening
primrose, and smartweed. Apply at least 45 days before planting. Add
surfactant at 0.25% on a volume basis. Do not enter treated fields for 12 hours
after application.
Roundup + 2,4-D (glyphosate+various trade names) Apply 0.5 - 1.5 + 0.5 - 1.0
lb. a.i./A for improved control of curly dock and cutleaf evening primrose. Apply
at least 2 weeks before planting depending upon the formulation. Add surfactant
at 0.25% - 0.5% on a volume basis. Do not enter treated fields for 12 hours after
application.
Gramoxone Extra + Harmony Extra (paraquat + thifensulfuron+tribenuron)
Apply 0.5 - 1.5 + 0.015 - 0.023 lb. a.i./A for improved control of curly dock, cutleaf
evening primrose, and smartweed. Apply at least 45 days before planting. Add
surfactant at 0.25% - 0.5% on a volume basis. Do not enter treated fields for 12
hours after application.
Gramoxone Extra + 2,4-D (paraquat + various trade names) Apply 0.5 - 1.5 +
0.5 - 1.0 lb. a.i./A for improved control of curly dock and cutleaf evening primrose.
Apply at least 2 weeks before planting depending upon the formulation. Add
surfactant at 0.25% - 0.5% on a volume basis. Do not enter treated fields for 12
hours after application.
Preplant Incorporated
Ordram 15G (molinate) Apply 3.0 - 4.0 lb. a.i./A to control barnyardgrass, annual
sedges, and suppression of red rice and large crabgrass. Incorporate in waterseeded rice on all soils and dry-seeded rice on finer textured/clay soils. Apply
immediately prior to flood establishment in water-seeded rice. Loss due to
volatilization may occur if not incorporated. Can also be applied by air into
floodwater in water-seeded systems. Do not apply where sensitive varieties are
grown. Do not enter treated fields for 12 hours after application.
Preplant Surface-applied
Bolero 8EC (thiobencarb) Apply 4.0 lb. a.i./A to control barnyardgrass, annual
sedges, and partial control of red rice. Apply after final seedbed preparation
immediately before flood establish in water-seeded rice. Water-seed rice early.
Avoid losing flood as water management is critical. Do not apply to sensitive
varieties. Do not enter treated fields for 4 hours after application.
Preemergence (Dry seeded)
Facet 75WP (quinclorac) Apply 0.33 lb. a.i./A (sandy soil), 0.5 lb. a.i./A (loamy
soil), or 0.67 lb. a.i./A (clay soil) to control barnyardgrass, morningglory, hemp
sesbania, and northern jointvetch. Facet does will not control sprangletop,
smartweed, or nutsedge. Apply after planting but before emergence. Make sure
seed are covered with soil. Adequate rainfall or flushing is needed for activation.
If soil dries, flush for reactivation. Has longer residual control than Bolero. Avoid
drift to susceptible crops. Do not enter treated fields for 12 hours after
application.
Delayed Preemergence (Dry seeded)
Bolero 8EC (thiobencarb) Apply 4.0 lb. a.i./A to control sprangletop, barnyardgrass, and aquatic weeds. Will not control emerged weeds or broadleaf
signalgrass. Apply 1 - 5 days before rice emerges. Adequate rainfall or flushing
is needed for activation. If soil dries, flush for reactivation. Control will generally
not exceed 3 weeks. Injury may occur if rice is stressed. Do not enter treated
fields for 4 hours after application.
Facet 75WP (quinclorac) 0.25 - 0.5 lb. a.i./A See comments above. Delayed
preemergence application may provide greater residual control relative to flood
establishment. Add 1 pt/A crop oil concentrate if weeds have emerged. Do not
enter treated fields for 12 hours after application.
Facet 75WP + Bolero 8EC (quinclorac + thiobencarb) 0.25 - 0.5 + 3.0 - 4.0 lb.
a.i./A. See comments above. Will broaden spectrum of control relative to the
individual herbicides listed above. Do not enter treated fields for 12 hours after
application.
Prowl 3.3EC (pendimethalin) Apply 0.75 - 1.0 lb. a.i./A to control sprangletop,
barnyardgrass, broadleaf signalgrass, and crabgrass. Use low rates for coarse
textured soil and high rates for fine textured soil. Apply 1 - 5 days before rice
emerges. Do not apply preplant incorporated or immediately after planting. Rice
seed must have imbibed water before application. Apply only after rainfall or
flushing for germination. Do not enter treated fields for 24 hours after application.
Facet 75WP + Prowl 3.3EC (quinclorac + pendimethalin) 0.25 - 0.5 + 0.75 - 1.0
lb. a.i./A. See comments above. Will broaden spectrum of control relative to the
individual herbicides listed above. Do not enter treated fields for 24 hours after
application.
Early Postemergence
Propanil (various trade names) Apply 3.0 - 4.0 lb. a.i./A to control barnyardgrass,
fall panicum, broadleaf signalgrass, hemp sesbania, northern jointvetch, rushes,
and annual sedges. Can be used in dry- or water-seeded rice, but foliage must
be exposed. Better control on small weeds with less than 4 leaves. Does not
have residual activity, so repeat applications may be necessary. Add 1 qt/A to
dry propanil formulations. Applying propanil with Facet, Bolero, or Prowl will
improve grass control. Avoid drift to susceptible crops. NOTE: Some
populations of barnyardgrass have developed resistance to propanil at rates as
high as 30 lb/A. Facet, Bolero, and Prowl can control these populations when
applied in a timely manner with appropriate water management. Do not enter
treated fields for 24 hours after application.
Arrosolo (propanil + molinate) Apply 2.25 - 3.0 + 2.25 - 3.0 lb. a.i./A to control
barnyardgrass, fall panicum, broadleaf signalgrass, hemp sesbania, northern
jointvetch, rushes, and annual sedge. Apply to emerged weeds. Do not apply to
rice that is not rooted in water-seeded systems. Provides better control than
propanil if environmental conditions are marginal (moisture stress and low
temperatures). Gives some residual weed control. Do not apply to Millie or
Adair. Do not enter treated fields for 24 hours after application.
Propanil or Arrosolo + Londax (propanil or propanil+molinate + bensulfuronmethyl) Apply 3 - 4 or 4.5 - 6.0 + 0.028 - 0.38 lb. a.i./A to control annual grasses,
yellow nutsedge, annual sedges, morningglories, hemp sesbania, northern
jointvetch, redstem, eclipta, and texasweed. Apply 1 - 7 days prior to
establishment of permanent flood. Weed must be exposed to herbicide. Use
caution with susceptible varieties. Application to rice with exposed roots may be
injured in water-seeded systems. Do not enter treated fields for 24 hours after
application.
Postemergence (Contact and residual control)
Propanil + Bolero 8EC (propanil + thiobencarb) Apply 3 - 4 + 3 lb. a.i./A to
control barnyardgrass, sprangletop, broadleaf signalgrass, fall panicum, hemp
sesbania, northern jointvetch, rushes, annual sedges, and aquatic weeds. If rice
is water-seeded, apply only after rice is well rooted and in the 2-leaf stage. Drain
flood or surface water from field before application. Application to rice stressed
by high salt and/or high pH soils may cause excessive rice injury. Rainfall or
flushing will be needed for activation if soil begins to crack. Provides up to 3
weeks residual control. Do not enter treated fields for 24 hours after application.
Propanil + Prowl 3.3EC (propanil + pendimethalin) Application rates are 3 - 4 +
0.75 - 1.0 lb. a.i./A. See comments under propanil + thiobencarb. Apply to
emerged weeds not covered by water. Drain flood or any surface water before
application. Rainfall or flushing will be needed for activation. Gives 2 -week
residual control. Residual control from Prowl may be reduced after flooding,
flushing, or several days of heavy rainfall. If used on water-seeded rice, do not
apply before the 3 - 4 leaf stage. Do not enter treated fields for 24 hours after
application.
Facet 75WP + Propanil (quinclorac + propanil) Apply 0.25 - 0.38 + 3 - 4 lb. a.i./A
to control barnyardgrass, broadleaf signalgrass, morningglories, hemp sesbania,
northern jointvetch, rushes, and annual sedges. See rate recommendations
above for Facet relative to soil type. Apply to small actively growing weeds. Add
crop oil concentrate at 1 qt/A if dry propanil formulation is used. Rainfall or
flushing may be required for activation or deactivation. Do not enter treated
fields for 24 hours after application.
Facet 75WP (quinclorac) 0.25 - 0.5 lb. a.i./A See previous comments above
concerning Facet especially when pertaining to rates relative to soil type. Add 1
qt/A crop oil concentrate. Apply to small actively growing weeds. Seed exposed
to the spray may be injured. Add propanil if weeds exceed 1-inch height.
Rainfall or flushing may be required for activation or reactivation. Fields treated
with Facet should be scouted for smartweed, nutsedge, and sprangletop and
treated if necessary. Do not enter treated fields for 12 hours after application.
Early Postemergence (Specialty use)
Propanil + Basagran (propanil + bentazon) Apply 3.0 - 5.0 + 0.75 lb. a.i./A to
control annual grasses, smartweed, cocklebur, redstem, yellow nutsedge,
dayflower, and spike rush. Will not control purple nutsedge. Apply to small
annual grasses, broadleaf and aquatic weeds and nutsedge. Propanil timing for
grasses should be applied as for propanil alone. Add 1 qt/A crop oil concentrate
if dry propanil formulation is used. For use in dry- or water-seeded rice. Gives
no residual control. Control of yellow nutsedge can be erratic. Do not enter
treated fields for 48 hours after application.
Propanil + Blazer (propanil + acifluorfen) Apply 3.0 - 4.0 + 0.125 - 0.25 lb. a.i./A
to control annual grasses, morningglories, and hemp sesbania. Apply when
hemp sesbania is 1 - 5 feet tall and morningglory runners are less than a foot
long. May cause tip burn on rice but injury usually does not last. Gives no
residual control. Do not apply more than 1 pt/A of Blazer per season. The
addition of Blazer can reduce propanil activity on grasses. Apply to small actively
growing weeds. For use in dry- or water-seeded rice. Do not enter treated fields
for 48 hours after application.
Propanil + Storm (propanil + bentazon+acifluorfen) Apply 3 - 5 + 0.5 + 0.25 lb.
a.i./A to control barnyardgrass, cocklebur, hemp sesbania, morningglories,
redstem, smartweed, and eclipta. Apply to small actively growing weeds. Gives
no residual control. For use in dry- or water-seeded rice. Storm may reduce
propanil activity on grasses. Do not enter treated fields for 48 hours after
application.
Grandstand (triclopyr) Apply 0.25 - 0.38 lb. a.i./A to control northern jointvetch,
hemp sesbania, morningglories, and alligatorweed. Apply to small actively
growing weeds. Can be applied when rice has 3 - 4 leaves up until 1/2 inch
internode elongation. Do not enter treated fields for 48 hours after application.
Grandstand + Propanil or Arrosolo (triclopyr + propanil or propanil+molinate)
Apply 0.25 - 0.38 + 3.0 - 4.0 or 2.25 - 3.0 + 2.25 - 3.0 lb. a.i./A to provide better
control than either of the herbicides alone. Do not include adjuvants with liquid
formulations of propanil or Arrosolo. Include crop oil concentrate with dry
formulations of propanil. Refer to labels for susceptible varieties. Do not enter
treated fields for 48 hours after application.
Ordram 15G (molinate) Apply 3.0 - 5.0 lb. a.i./A to control barnyardgrass,
dayflower, sprangletop, annual sedge, and suppression of spike rush. Apply to
barnyard-grass 3 - 24 inches or sprangletop 8 inches or less. Apply to flooded
field and maintain flood until grass is controlled. The smaller the grass or the
longer the flood on the longer grass, the better the suppression. Do not apply to
sensitive varieties. Do not enter treated fields for 12 hours after application.
Londax (bensulfuron-methyl) Apply 0.038 - 0.0625 lb. a.i./A to control ducksalad,
redstem, eclipta, false pimpernel, gooseweed, dayflower, flatsedge, water
hyssop, and arrowhead. Apply within 5 days after flooding and maintain flood at
least 7 days. For water-seeded rice, apply as soon as possible after rice has
pegged and flood has stabilized. Avoid pumping for 7 days after treatment, if
possible. If weeds have emerged, add 1 qt/A crop oil concentrate. Do not enter
treated fields for 24 hours.
Permit (halosulfuron-methyl) Apply 0.5 - 1.0 lb. a.i./A to control annual and
perennial sedges, hemp sesbania, and jointvetch. Does not control grassy
weeds. The label prohibits post-flood application. Permit may be tank mixed
with other postemergence herbicides to broaden weed control spectrum. Do not
enter treated fields for 12 hours after application.
Whip (fenoxaprop-p-ethyl) Apply 0.059 - 0.067 lb. a.i./A to control grassy weeds
such as sprangletop and barnyardgrass. Water management is critical, and
performance is dependent upon environmental conditions. Can injure sensitive
varieties. Do not enter treated fields for 24 hours.
Postemergence (Broadleaf and aquatic weed control at midseason)
2,4-D (various trade names) Apply 1 - 1.5 lb. a.i./A of 2,4 -D to control broadleaf
and aquatic weeds. Apply between the first internode elongation (first green ring)
and 1 /2 inch long internode elongation (second green ring). Do not apply when
internode exceeds 1 /2 inch. Adhere to restrictions on 2,4-D application in north
Louisiana. Adhere to individual label specifications for pre-harvest restrictions
and restricted entry intervals.
Grandstand (triclopyr) 0.25 - 0.38 lb. a.i./A of triclopyr to control broadleaf and
aquatic weeds. Does not control ducksalad. Triclopyr may be applied from the
3- to 4-leaf stage up to 1/2 inch long internode elongation. Apply within 2 weeks
of harvest. Do not enter treated fields for 48 hours after application.
Blazer (acifluorofen) Apply 0.125 - 0.25 lb. a.i./A to control hemp sesbania at 1 5 feet. Do not apply past the boot stage of rice. May cause tip burn on rice, but
symptoms are quickly outgrown. Do not apply within 45 days of harvest. Do not
enter treated areas for 48 hours.
Preharvest
Sodium Chlorate (various trade names) Apply 6 lb. a.i./A for the desiccation of
green weed foliage when average moisture is 25% or below. Harvest within 7
days after application to prevent overdrying. Do not enter treated areas for 12
hours.
Ratoon Crop
Hi-Dep 2,4 -D Apply 0.47 - 0.95 lb. a.i./A to control most broadleaf weeds. Apply
within 2 weeks of first harvest. A shallow flood should be present at time of
application. Do not enter treated fields for 48 hours after application.
Grandstand (triclopyr) Apply 0.38 lb. a.i./A to control northern jointvetch, hemp
sesbania, and other broadleaf weeds. Does not control ducksalad. Apply within
2 weeks of harvest. Do not enter treated fields for 48 hours after application.
Basagran (bentazon) Apply 1.0 lb. a.i./A to control sedges and some broadleaf
weeds. Apply to small weeds less than 8- to 10-inches tall. Do not enter treated
fields for 48 hours after application.
Newer Herbicides
Newpath (imazethapyr) Apply 0.0625 lb. a.i./A for excellent control of red rice,
grassy weeds, and nutsedge. Gives fair control for a short list of broadleaf and
aquatic weeds but is weak on hemp sesbania and jointvetch. For complete
control of red rice, two applications are required. Newpath must be applied
preplant incorporated or preemergence and postemergence prior to permanent
flood only to Clearfield (imidazolinone-tolerant) varieties. Postemergence
applications require nonionic surfactant at 0.25% on a volume basis. Application
timing and water management are critical. Adequate soil moisture is required for
optimum herbicide activation for all methods of soil application. Newpath must
be applied pre-flood when rice is in the three- to five-leaf growth stage.
Permanent flood should be initiated within two days after postemergence
applications. There should be an interval of at least 45 days between Newpath
application and harvest. Do not enter treated fields for 12 hours after application.
Command (clomazone) Apply 0.4 - 0.6 lb. a.i./A preemergence to earlypostemergence for annual grass control. Application window is 1-2 leaf rice.
Rate depends on soil type with higher rates used on heavier soils. Do not use
post-flood. Not recommended for coarse soils. Small and medium grain rice is
more susceptible to injury. Observe label for rotational and application
restrictions. Do not enter treated fields for 12 hours after application.
Ricestar (fenoxaprop-p-ethyl) Apply 13 - 17 fl. oz. per acre before tillering stage
of rice to control annual grassy weeds such as barnyardgrass, fall panicum, and
sprangletop. It does not control broadleaf weeds. Do not use surfactant.
Ricestar is essentially Whip with a safener. Ricestar can be used post-flood.
Observe label for rotational and application restrictions. Do not enter treated
fields for 24 hours after application.
Regiment (bispyribac sodium) Apply 11.25 - 15 g product/A postemergence for
most broadleaf weeds and barnyardgrass after the 3-leaf stage o f rice. Regiment
has demonstrated good activity on rice flatsedge and hemp sesbania at low use
rates. However, it is weak on broadleaf signalgrass and sprangletop. Regiment
can be applied post-flood. Do not enter treated fields for 12 hours after
application.
VERTEBRATE PESTS
Blackbird Management
Blackbirds (Icterinae) are among the most numerous birds in rice-growing
areas. The red-winged blackbird (Agelaius phoeniceus) is the most abundant
breeding bird in the rice-growing area of southwestern Louisiana. Red-winged
blackbirds are responsible for most rice depredation. Brown-headed cowbirds
(Molothrus ater), common grackles (Quiscalus quiscula) and boat-tailed
grackles (Quiscalus major) cause the rest of rice damage. Blackbirds can be
responsible for significant economic loss during sprouting and ripening stages
each year. Damage to sprouting rice can be particularly severe in water-seeded
rice. Economic losses caused by blackbird damage are most severe in fields
located within five miles of winter roost sites. These areas are traditionally
adjacent to coastal marshes.
Both federal and state governments recognize that blackbirds are important
depredators of agricultural commodities. Blackbirds are migratory birds and are
provided protection under provisions of the Migratory Bird Treaty Act. They may
be controlled without a federal permit when found depredating agriculture crops.
No conventional agricultural pesticides are labeled for use in reducing
blackbird damage in rice production. No lethal chemical compound that will
control blackbirds in agricultural crops safely and effectively is likely to be
registered for general use by producers in the near future. Methods of control
involve alternative cultural practices, scare devices, chemical repellents and
restricted use toxicants.
Cultural Practices
1) Drill seed rice on a well-prepared seedbed. Water-plant only where a
continuous uniform flood of 2 - 6 inches can be kept on the rice.
2) Delay planting rice in high blackbird infested areas (such as coastal
areas) until after April 1. Arrange planting programs so fields near roost
areas or coastal marshes are planted last. Begin planting nearest the
farm headquarters and progress to more sensitive areas later in the
season.
3) Block planting in areas of traditionally severe bird damage, such as in
fields adjacent to coastal marshes, can be effective in reducing damage
on individual farms. This method requires that a group of farmers in a
given area plant all or most of their rice on, or near, the same date.
4) Consider alternate crops in high bird pressure areas where there has
been a history of extreme damage to rice crops.
5) Habitat modification and clean cropping may be helpful in reducing the
number of resident blackbirds damaging rice crops at maturity. Removing
brush and trees from ditch banks, levees, fence rows and keeping fields
free of weeds will eliminate blackbird habitat in and around field areas.
Scare Devices
Propane exploders with timers to turn them off and on automatically each
day are the most effective scare devices used to move feeding blackbirds from
freshly planted rice fields and after maturity. There should be a least one
exploder for every 25 acres of crop to be protected. They should be elevated
on a barrel, stand or truck bed to “shoot” over the crop. They should be moved
around the field every few days. Exploders should be reinforced with live
ammunition fired from shotgun and .22 caliber rifles. In addition, pyrotechnics
such as 12-gage shell crackers, rope fire crackers and rocket bombs can be
helpful when used with live ammunition and propane exploders.
Chemical Repellents
1) Chemical repellents are compounds that must be registered by EPA.
When placed on rice seed or other bait, repellents will deter consumption
of newly planted seed by blackbirds. They work by causing olfactory,
gustatory, or digestive irritation in the target animal. At present, no
chemical repellents are registered to protect newly planted rice seed.
2) Methyl anthranilate under the trade name of Bird Shield™ is a chemical
compound that holds promise for protecting seed rice.
Restricted Use Toxicants
1) Avitrol (4-aminopyridine) is a poison with flock-alarming properties used
to control blackbirds and starlings in, on or around the area of feedlots,
structures, nesting, roosting and feeding sites. It acts in such a way that
only a part of the flock feeding on the bait will ingest treated bait, react and
frighten the rest away. Birds that react and alarm a flock usually die.
Avitrol is for sale to and use only by certified applicators or persons
under their direct supervision and only for those uses covered by the
Certified Applicators Certification. Distribution of Avitrol should be limited
to scattered spot placements that will provide feeding opportunities only
for the necessary number of target birds. After the birds’ feeding pattern
has been established through prebaiting, untreated bait is removed and
diluted treated bait applied only at sites where the target birds are actively
feeding. Do not apply this product where non-target bird species are
feeding. Treated bait should be picked up and removed from the field
each day.
2) Compound DRC-1339 is an avicide registered for use in parts of the
southern region under a 24 (C), local needs label. Only personnel of the
USDA Animal Damage Control Program and those working under their
supervision can use it. DRC-1339 is applied to brown rice baits broadcast
on blackbird staging areas near winter and spring roosting sites.
Depending on the number of birds killed, the product is sometimes
effective in reducing rice depredations associated with large
concentrations of roosting blackbirds. DRC-1339 has not been effective
when used in areas where blackbirds are widely dispersed.
Lesser Vertebrate Pests
Occasionally other vertebrate pests invest some rice fields. Among these
are feral hogs, nutria, and beavers. The damage is usually not direct but
interferes with other cultural practices involved in growing the crop. Several of
these pests, as in the case of nutria and beavers, interfere with water
management by damaging ditch banks and levees. Beaver dams around drains
can cause fields to flood excessively. Damage by feral hogs is more direct, and
in isolated cases, severe. In rare but extreme cases these animals must be
removed by either trapping, or in the case of feral hogs, hunting.
POST HARVEST PESTS
Insects
Many types of insects attack small grains in storage. Because small grains
are usually harvested in late spring and early summer and stored when
temperatures are high, insects can develop rapidly within the grain. Therefore,
insect problems in storage are more severe in small grains than in other grains,
such as corn, that are harvested and stored during cooler fall and winter months.
If a problem occurs, the first step is to identify the insect pest. Producers not
familiar with stored-grain pests should consult their county extension agent for
assistance.
Primary Feeders
Weevils
The rice weevil (Sitophilus oryzae) is about 1 /8 inch long and are reddish
brown to almost black. The wing covers are usually marked with four reddish or
yellow spots. Eggs are laid within individual kernels, and the grub -like larvae
consume the grain from within. Pupation occurs in the kernel, and adults leave
through a small round hole, leaving behind a hollow kernel. During warm
weather, an entire generation may be completed within 26 days; thus, stored
grain may be severely damaged within a month of harvesting. Infestations may
start near the top of a storage bin (as a result of insects that fly in from outside)
or near the bottom (caused by insects that migrate up through the perforated
floor). Weevils are very mobile and may be found anywhere within the grain
mass.
Lesser Grain Borer
Adult a nd larval stages of the lesser grain borer (Rhyzopertha dominica)
feed on and within kernels. The beetles have a slender, cylindrical form, with the
head turned under the body. They are dark brown or black and are slightly less
than 1/8 inch long. Eggs are laid in the grain. After they hatch, the young larvae
feed upon debris or flour produced by the boring beetles. In a short period,
larvae bore into the kernels and feed from within. Lesser grain borer populations
can build up rapidly in warm weather and can cause significant losses. The
beetles can develop throughout the grain mass and cause weevil-like damage.
Grain Moths
Indian meal moths and Angoumois grain moths usually feed on the
exposed sur face of the stored grain mass. They rarely penetrate more than 1
foot beyond or below the surface. Therefore, their damage potential is somewhat
limited. However, damage and contamination from these insects can cause an
economic loss.
The Angoumois grain moth (Sitotroga cerealella) is a small, buff-colored or
yellowish brown moth with a wing span of about 1/2 inch. Infestation may occur in
the field or within bins. Under normal circumstances, eggs are laid on the outside
of the grain and the larvae bore into and develop within the grain. The larvae are
small, white caterpillars with yellowish heads and grow to 1 /4 inch long. An
important identification characteristic of this insect is the small round emergence
hole the adult produces as it leaves each infested kernel.
Indian meal moth (Plodia interpunctella) caterpillars feed from the outside
of the kernel and primarily destroy the germ. They also feed on dust, chaff, and
broken kernels. Thus, they are more of a threat to seed grain than grain
intended for feeding purposes. The moths have a wing span of about 3/4 inch
with reddish brown to copper-colored markings on the outer 2 /3 of the front wings.
Larvae are dirty white, about 1 /2 inch long, and may produce a great deal of
webbing. They stay on the surface of the grain and do not develop deep within
the grain mass. Severe infestations are covered with large amounts of surface
webbing that may clog unloading and grain-handling equipment.
Secondary Feeders
The saw-toothed grain beetle (Oryzaephilus surinamensis) adult is a small,
active, brown beetle, 1 /8 inch long, with a flattened body and six saw-toothed
projections on each side of the thorax. The larva is yellowish-white, about 1/8
inch long, with a brown head. The abdomen tapers toward the tip.
The flat grain beetle (Cryptolestes pusillus) is about 1/16 inch long and is
one of the smallest beetles commonly found in stored products. It has a greatly
flattened body with antennae about 2/3 as long as the body. Both larvae and
adults have chewing mouthparts.
Management
Pre-storage Procedures
Insect management for stored grain depends upon good sanitation and
grain storage practices. Clean grain-handling equipment before harvest. Clean
nearby feed storage areas, feed rooms, and similar areas to reduce the potential
for insect migration into the new, non-infested grain.
Before harvest, thoroughly clean inside, around and under the empty bin.
Although it may be difficult and time-consuming to remove and clean under the
perforated floor, most insect problems originate in carryover material from this
area. The floor should be periodically taken up, if possible. Spray the bin walls,
roof, and floor to the point of runoff with Tempo, Reldan 4E, or Malathion. Be
sure to treat cracks, crevices around doors and behind false partitions, and
similar voids.
Reldan 4E (Chlorpyrifos-methyl) – 8 oz. per 6.5 gallons of water using 1 gallon
finished spray per 650 sq. ft. to 1250 sq. ft.
Tempo (Cyfluthrin) – Mix 0.05% solution and spray 1 gallon per 1000 sq. ft.
Malathion (various) – 1 gallon of a 57% EC in 25 gallons of water.
Protecting Stored Grain
Apply liquid grain protectants to the grain as it is being augured into the bin
to ensure adequate coverage. Reldan at 9 oz. per 5 gallons water per 1000
bushels is a popular approved grain protectant. Bacillus thuringiensis (Bt)
(consult label) should be applied to control Indianmeal moths.
Inspect the grain at monthly intervals (weekly when the temperature is
greater than 60o F). Use probes and appropriate equipment to monitor
temperature, moisture, and insect presence at several sites and depths. Even
when outdoor temperatures are low, moisture, insects and sunlight may produce
areas within the grain mass that are warm enough to allow insect development.
Therefore, be sure to inspect the grain frequently and thoroughly.
Fumigation
Aluminum phosphide (Phostoxin, Fumitoxin, etc., check labels) is best in
most circumstances for fumigation of infested grain. Five days in a very tightly
sealed storage are normally required for aluminum phosphide fumigation,
depending on temperature.
Fumigation is tricky and potentially dangerous. It should be done
professionally unless the producer knows how to do it right, has the
equipment to do it properly, and is properly certified. Careless or
uninformed fumigation can result in death.
Diseases
Certain diseases caused by fungi occurring in the field may be carried over
upon storage and processing. These are controlled by drying the rice at harvest
and maintaining proper moisture content in the bins.
TIMELINES
Worker Activities
Mar
Apr
May
June
July
Aug
Sept
Crop Growth Stages
Mar
Apr
May
June
July
Aug
Sept
Apr
May
June
July
Aug
Sept
pesticide
application
weed
monitoring
insect
monitoring
disease
monitoring
vertebrate
monitoring
mechanical
harvest
seeding
tillering
internode
formation
prebooting
booting
heading
grain filling
Insects
Mar
rice water
weevil
rice stalk
borer
sugarcane
borer
rice stink bug
rice seed
midge
chinch bug
fall armyworm
rice leaf miner
aphids
grasshopper
insecticides
Weeds
Feb
barnyardgrass
signalgrass
red rice
sesbania
alligatorweed
dayflower
ducksalad
redstem
Mar
Apr
May
Jun
Jul
Aug
jointvetch
sedges
knotgrass
sprangletop
morningglory
Texas weed
eclipta
smartweeds
herbicides
Diseases
Mar
bacterial leaf
blight
blast
brown spot
crown rot
crown sheath
rot
downy mildew
false smut
grain spotting
kernel smut
Apr
May
Jun
Jul
Aug
Sept
leaf scald
leaf smut
narrow leaf
spot
seedling blight
sheath blight
sheath spot
stackburn
stem rot
water mold
seed rot
white tip
sheath rot
fungicides
Cultural Practices
Feb
Delayed
Flood
seedbed
preparation
seeding
fertilization
flooding
Pinpoint
Flood
seedbed
preparation
seeding
Mar
Apr
May
Jun
Jul
Aug
fertilization
flooding
Continuous
Flood
seedbed
preparation
seeding
fertilization
flooding
REFERENCES
Crop Protection Reference. 2002. C&P Press. New York. 2391 pp.
Louisiana Rice Production Handbook. 1999. Louisiana Cooperative Extension
Service. Louisiana Agriculture Experiment Station. LSU AgCenter. Publication
number 2321. 116 pp.
Rice Production Best Management Practices. 2000. Louisiana Cooperative
Extension Service. Louisiana Agriculture Experiment Station. LSU AgCenter 19
pp.
Rice Production Handbook. 2001. Cooperative Extension Service, University of
Arkansas. Publication number MP 192. pp. 126 pp.
Rice Varieties and Management Tips. 2002. Louisiana Cooperative Extension
Service. Louisiana Agriculture Experiment Station. LSU AgCenter. Publication
number 2270. 24 pp.
2002 Rice Production Guidelines. 2002. Texas Cooperative Extension Service.
The Texas A&M University System. Publication number D-1253. 58 pp.
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