March 4, 2002 http://commodities.caes.uga.edu/fieldcrops/cotton
IN THIS ISSUE:
Cover Management in
Conservation Tillage
Insect Management
Decisions Before and at Planting
Early Management
Decisions for Controlling Disease and Nematodes in Cotton
Avoiding 2,4-D Injury to
Cotton
Cover Management in Conservation Tillage. (Brown) Winter vegetation management in conservation tillage systems
requires consideration of several factors.
The primary goal is to establish a reasonable stand of cotton, and that
single goal influences all other decisions related to cover management.
The following are potential benefits or
desirable characteristics of vegetative covers.
Provide soil and water conservation in winter
months.
Vegetation can be winter weeds or small grain or legume cover
crops. Winter weeds are no-cost inputs
which frequently provide erosion control during winter months but rarely
persist enough to offer wind or soil protection once the crop is
established. The USDA definition for
“conservation tillage” is a system that provides a residue cover on the soil
surface of at least 30 percent immediately after planting. Seeded cover crops in descending order of
use in Georgia include wheat, rye, oats, and crimson clover. There are only a few plantings of lupine and
vetch.
Ease of elimination through natural desiccation
or application of burndown herbicides. Among the most critical aspects of successful
cotton establishment and early season growth is the elimination of all existing
vegetation. Weeds or cover crops that
are hard to kill with burndown herbicides disrupt the entire production system. Vigorous winter weeds, cover crops, and
emerged warm season weeds pose a serious competitive threat to seedling cotton.
Winter weeds such as cutleaf eveningprimrose, horseweed, and wild radish are
difficult to kill in April and May with standard burndown products (glyphosate
or paraquat), but 2,4-D applications in February to early March are highly
effective and economical on these troublesome broadleaf species. In general, small grains are easier to
eliminate with burndown herbicides than legumes, though in some systems, early
maturing crimson clover may produce seed and decline sufficiently early to make
burndown treatments unnecessary.
Another generalization is that when small grains are actively growing,
glyphosate is probably superior to paraquat treatments, but as seed heads
appear, paraquat is equally effective.
Ryegrass is an easy to establish, aggressive cover but it is sometimes
very, very difficult to kill in the spring.
Produce direct or indirect cash value in
grazing, seed production, or N fixation. Cover crops can provide significant value in
addition to soil and water conservation and wind protection. Small grains can be used for grazing or
grain. Compaction associated with
cattle grazing has not been a limiting factor in strip-till cotton. Double crop systems have worked well in south
Georgia, but once every 7 to 10 years, an early frost curtails the cotton
season. Legumes provide a source of
“free” N (at least 30 lb/A) through the natural process of fixation, and
crimson clover has worked well in a reseeding system in which the legume
matures and produces seed for future years prior to the establishment of
cotton.
Provide soil and water conservation and wind
protection in the spring/summer months. Persistence of residue is important in
maintaining conservation properties of covers into the cotton season. Small grain straw is more persistent than
clover or vetch residue. For small
grains, the more aggressive, earlier growth of rye provides more residue than
wheat. Termination date of small grain
covers, which obviously affects the amount and persistence of residues, must
balance the calendar in respect to target date for planting cotton and the
amount of residue. From the standpoint
of cover desiccation and potential problems with insects, burndown applications
should be made at least 3 weeks prior to planting cotton. Early termination allows the cover to dry
down; it permits re-treatment if necessary; and it removes host plants for
insects. How much residue is too
much? Excessive cover or residue can
physically interfere with strip-till and planter operations. With experience and tinkering, some growers
can successfully work in an incredible amount of rye residue. However, those just moving into conservation
tillage might consider burning down rye before it exceeds 3 to 4 ft in height
and wheat before it reaches 2 or 3 ft.
Generally, size and growth dictate termination date for rye, while the
calendar (cotton planting date) determines the time to treat wheat. Terminating too early greatly diminishes
residue even to the point of its total disappearance shortly after cotton
emergence.
Vegetative covers sometimes adversely affect
cotton. Covers can harbor pest
organisms and negatively affect soil moisture levels in the spring. Some legumes are a host for nematodes, a
group of pests which are having more and more of an impact across the
state. Legumes, and to a lesser degree
small grains, can be a reservoir for insects such as cutworms, false chinch
bugs, and occasionally grasshoppers.
Residues may create a few more problems with seedling diseases, though
this has proven to be a minor issue.
Degradation of legumes can release certain compounds that are harmful to
young cotton plants, hence the benefit of an interval of 3 weeks between
burndown application and planting. Spring
growth of cover crops can significantly deplete soil moisture, a serious
problem in years with deficit rainfall in the winter and spring. Early termination partially alleviates this
problem. In wet years, covers,
especially legumes, can maintain a wet mat at the soil surface and thus
complicate strip-tillage and planting.
The total value of cover crops goes well beyond
immediately measurable benefits. Long
term advantages include sustained soil and water conservation, organic matter
buildup, increased water infiltration, improved soil tilth, reduced crusting,
etc. Such benefits become increasingly
apparent after several years in conservation tillage systems and undoubtedly
enhance land productivity and overall management.
Insect Management Decisions Before and at
Planting - (Roberts) Variety selection may be the single most
important decision a producer makes in a given year. In addition to factors such as yield and quality, growers must
also give consideration to available transgenic traits such as Roundup Ready
and Bollgard. From an insect management
standpoint, decision to plant Bt or not-Bt cotton will greatly influence IPM
for the upcoming year. Factors to consider
concerning whether or not to plant Bt cotton include tobacco budworm populations,
the threat of pyrethroid resistance, and your ability to treat tobacco budworm
and corn earworm in a timely manner in the presence of high pressure.
Pyrethroid resistant tobacco budworm was first
documented in Georgia during 1997 in Decatur County. Since that time we have observed problems with control and
suspect resistance or increased tolerance in other parts of the state. Alternative insecticides such as Tracer and
Steward are effective tools for managing pyrethroid resistant tobacco budworm. However, foliar treatments must be applied
on a timely basis. Larvae less than 1/4
inch in length (3 days of age) must be targeted to achieve good control. Non-Bt acres should not exceed what can be
sprayed in 3-4 days. If we experience
high pressure, multiple insecticide applications of insecticide may be needed
on a five- day interval. Rain and other
delays may inhibit our ability to be timely and reduce the effectiveness of
insecticide applications. We have the
tools to manage tobacco budworm and corn earworm on non-Bt cotton, but
management will be more intensive.
Regardless of technology, a good scout is a must. Good decisions can only be made when we have
good scouting information.
Many growers have increased acreage of
conservation tillage during recent years.
Variations in insect complexes can vary by tillage system. Many insects are unaffected by tillage
system and include most mid-late season bug and caterpillar pests. Early season thrips populations are
generally lower in reduced tillage but a preventive insecticide at planting is
still recommended. However, the risk of
attack from some insect pests, especially cutworms, is increased in conservation tillage. The risk of cutworm attack can be significantly reduced if winter
cover crops or weeds are terminated at least 3 weeks prior to planting. If the cover is not terminated, cutworms may
become established on plants and move to emerging cotton seedlings as host
plants dry down. Observations and data
suggest timely termination is especially important when legumes or winter weeds
are used as the cover. In addition to
cutworms, problems with false chinch bugs have been observed in recent
years. Most problem fields have been in
reduced tillage and high populations tend to be associated with fields which
were not burned down in a timely fashion.
In situations where the risk of cutworm attack is high (i.e. following
legumes or green vegetation present at planting) consideration should be given
to applying a preventive cutworm treatment at planting. An economical approach would be to band a
pyrethroid behind the planter.
On a more limited basis we have observed some
fields with high populations of grasshoppers.
Timely termination of covers will help here but will not eliminate the
threat of stand reduction from grasshopper feeding.
One very obvious difference in conservation
tillage is the build up of fire ant populations due to the lack of soil
disturbance. Fire ants are an important
predator of bollworm eggs and larvae.
We consider fire ants to be one of the three most important predators
which would also include bigeyed bugs and minute pirate bugs. However, there is a slight negative
associated with fire ants. Fire ants
feed on honeydew excreted by aphids and will protect or farm aphids so as to
increase the presence of honeydew. The
end result is that aphids tend to build populations quicker in the presence of
fire ants, but these same fields are generally the first in which aphids crash
due to the naturally occurring fungus.
The benefits of fire ants far outweigh this slight negative. From an IPM standpoint, termination of the
winter cover at least three weeks prior to planting will reduce the risk of
early season insect problems.
A preventive insecticide at planting is recommended
for early season thrips control. There
are several options available which include in-furrow granules, in-furrow
sprays, and seed treatments. A large
percentage of the acreage in Georgia is treated with Temik in-furrow. Temik at 3.5 lbs product per acre has proven
to be a consistent performer.
Commercial seed treatments offer convenience at planting and are an
option for early season thrips management.
Orthene treated seed provide control for about 7-10 days. Gaucho and Cruiser (formerly Adage) will
provide more extended control. However,
these seed treatments have tended to be erratic in performance when compared
with Temik. This erratic performance
appears to be more common on April and early May plantings when thrips
populations are generally high and plant growth may not be rapid. Regardless of treatment applied at planting,
it is important that growers scout fields at least weekly and react in a timely
fashion if the treatment is failing.
Foliar sprays of Orthene, Bidrin, or dimethoate are recommended when
thrips number 2-3 per plant. Foliar
treatment is rarely necessary after plants have 5 true leaves and are growing
rapidly.
Early Management Decisions for Controlling
Disease and Nematodes in Cotton - (Kemerait) Diseases and nematodes are likely to cause
at least some concern for many of Georgia=s cotton growers in 2002. One of the most difficult issues in the
management of these problems is that decisions must be made before (sometimes
long before) symptoms appear in the field.
For example, though we are still a couple of months from planting,
growers are likely committed to a crop rotation scheme for the 2002 season and
either did or did not pull nematode samples last fall. If they did pull the samples, they have some
idea of nematode populations in their field, otherwise they must rely on notes
or memories from previous seasons.
At this point, growers must decide whether or
not to use a nematicide to reduce damage from root knot, reniform, sting, and
Columbia lance nematodes. Obviously, if
they haven=t had a problem in the past, or are coming off a very good rotation
(e.g. several years out of a host crop), then they may not need a
nematicide. However, if they are going
into a field with a history of damage and loss, then they need to decide 1) if
they can afford to put out a nematicide (can they afford not to?), 2) which
nematicide to use (probably Telone II or Temik 15G), and 3) which rate to
use. Once the seed is covered, it is too
late to make many other nematicide decisions.
Breaking up an existing hard pan before planting and adequate irrigation
during the season will also help reduce losses to nematodes.
Seedling diseases are generally not an important
problem for most growers in the state.
However, seedling diseases hit a few farmers hard every year and these
growers need to think about using a fungicide treatment in addition to what
already is formulated on the seed. They
also need to determine if previous losses have been from Rhizoctonia or Pythium
(or both), as these pathogens are not necessarily controlled by the same
fungicides. Seeds planted into cool,
wet soils are most at risk; growers can minimize the risk by waiting to plant
until conditions improve. Data from
2002 showed that in-furrow fungicides such as Terraclor and Terraclor Super X,
as well as hopper box treatments, often improved stand counts, but
corresponding increases in yield did not occur. At-risk growers should carefully weigh their options to reduce
seedling disease before they plant. Again,
once the seed is covered, there aren’t any future options.
Fertility plays a role in boll rot and in Stemphyllium leaf spot, both of which can be devastating. Growers should carefully follow fertility recommendations to avoid excessive amounts of nitrogen that can lead to rank growth and boll rot. Growers should also insure adequate levels of potassium as low potassium levels are the primary cause of Stemphyllium leaf spot.
Avoiding 2,4-D Injury to Cotton
- (Culpepper) Cotton injury from
2,4-D continues to be a common and unnecessary problem. The problem can result from sprayer
contamination, spray drift, and vapor drift.
Special
thanks to Dr. Alan York of NC State University for help in preparation of this
section.
Cotton injury can occur from minute residues of
2,4-D (or 2,4-DB) in a sprayer. It is
recommended that any sprayer previously used to apply 2,4-D not be used in
cotton. If such a sprayer must be used,
it should be washed thoroughly before spraying cotton. Special attention should be given to
sprayers used to apply Roundup Ultra or emulsifiable concentrates because these
products seem to be particularly effective at pulling 2,4-D residues out of a
sprayer.
The following procedure is suggested for washing
out sprayers that have been used to apply 2,4-D. Keep in mind this procedure may not totally remove 2,4-D
residues. Dispose of rinsates in an
approved manner.
1.
Remove nozzles, nozzle strainers, and in-line
strainers. Using a soft brush, wash the
nozzles and strainers with soapy water.
Be sure to remove any visible deposits.
2.
Before replacing nozzles and strainers, fill
sprayer tank with water and add a strong detergent such as 4 pounds of
trisodium phosphate per 50 gallons of water or a commercial spray tank
cleaner. Agitate for 15 minutes and
then flush about one-fourth of the water-detergent mixture through the
lines. Replace nozzles and strainers
and flush remainder of water-detergent mixture through the nozzles.
3.
Spray diesel fuel on the inside surfaces of the
tank. Start the sprayer to fill the
lines, and let the diesel fuel sit in the lines for several hours, preferably
overnight. Then spray out the diesel
fuel. Note: this step is suggested only
if the sprayer has previously been used to apply an ester formulation of 2,4-D.
4.
Fill the tank with water and add household
ammonia at the rate of 1 quart per 25 gallons of water. Agitate for 15 minutes, spray a few gallons
of the mixture through the nozzles, and let the remainder sit in the tank and
lines for several hours, preferably overnight.
Then spray out the remainder of the ammonia-water mixture.
5.
Fill the tank with water and detergent. Agitate for several minutes and spray it
out.
6.
Fill the tank with fresh water and spray it all
through the nozzles.
Spray drift means movement of spray droplets by
wind. As opposed to vapor drift
(described below), spray drift can occur with any formulation of 2,4-D (or any
other product). Spraying during windy
conditions and using nozzles and pressures that result in the creation of fine
spray droplets increase the risk of spray drift.
Except in extreme cases, such as spraying in
very windy conditions and using nozzles and pressures that create very fine
droplets, spray drift normally is observed only over short distances. A buffer of 200 feet or more between the
area being sprayed and the susceptible crop usually is adequate to prevent
injury from spray droplet drift unless it is very windy. If there is no wind or if the wind is
blowing away from the cotton field, a shorter buffer is acceptable.
Most cases of 2,4-D injury to cotton result from
vapor drift of an ester-containing formulation of 2,4-D. Vapor drift results when the herbicide
volatilizes and the vapors move to a susceptible crop such as cotton. Hot temperatures, moist soils, and thermal
inversions all increase the potential for vapor drift. Injury from vapor drift can occur at rather
long distances from the sprayed area.
Vapor drift can be avoided simply by refraining
from the use of ester-containing formulations of 2,4-D. Ester formulations should not be used within
a mile of any cotton field during the months that cotton is in the field. Most commercially available ester
formulations are considered Alow volatile.@
These formulations are still volatile, and their use can lead to cotton
injury. Weedone 638 and any other
formulations containing a mixture of 2,4-D ester and 2,4-D acid also should be
avoided in cotton-producing areas.
Vapor drift usually is not a problem with amine formulations of 2,4-D.
Ester and ester-acid formulations of 2,4-D are
popular because they mix well with liquid nitrogen. Amine formulations also can be mixed with liquid nitrogen if the
2,4-D is premixed with water before adding it to the liquid nitrogen.
Edited by:
Contributions by:
Steven M. Brown, Extension Agronomist-Cotton
Stanley Culpepper, Extension Agronomist-Weed
Science
Bob
Kemerait, Extension Plant Pathologist
Phillip Roberts, Extension Entomologist
COLLEGE OF AGRICULTURAL AND ENVIRONMENTAL SCIENCES, COLLEGE OF FAMILY AND CONSUMER SCIENCES
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SCHOOL OF FOREST RESOURCES, COLLEGE OF VETERINARY SCIENCES
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