UGA Cotton Newsletter --October 25, 2000

Crop Situation 1

2000 Season Disease Assessment 2

Variety Distribution of the 2000 Crop 3

Nematode Management Begins with a Soil Sample 3

Changes at the UGA Extension Nematology Laboratory 4

Georgia Ag Statistics Service Conducts Cotton Grower Survey 5

Calendar 5

Crop Situation. (Brown) As of October 20, about 40 percent of the anticipated crop has been harvested. We are projected to harvest between 1.2 and 1.3 million acres and produce a yield of around 600 lb/A. Yields and fiber and seed quality have suffered because of adverse weather during the growing season and harvest The October 20 report from the USDA Classing Office in Macon indicates various fiber parameters of the crop thus far, and reveals improvement in color grade over previous weeks. As of this date, 54 percent of the crop is short staple (less than 34/32nds) and 12 percent is high micronaire (above 4.9).

Fiber Quality of Bales Classed at the Macon Classing Office
Color Grade 41 or better (% of Crop) Bark/Grass

(% of Crop)

Average Staple Average Leaf Grade Average Strength Average Mic Average Uniformity
54 2 / 2 33.4 3.0 27.2 4.6 80.8
Based on 248,180 bales classed through October 20, 2000.

Yields in many irrigated fields have been at least a couple hundred lb/A less than expected. This has been reflected in grower fields across the state and in research trials. For example, highest plot yields in several variety tests in Tifton ranged from 940 to 730 lb/A; similarly, large plot yields from Sun Belt Expo topped out at only 800 lb/A. Production of the highest yielding varieties in these tests commonly exceed 1150 lb/A and rarely fall below 1000 lb/A.

Comments about a couple of causes and explanations for depressed yields are warranted.

(1) Boll rot and hard lock were widespread as a result of the rain, high humidity, and overcast weather that occurred in September. Rainfall amounts across the state averaged 7 to 30 inches during the first 3 weeks of September when much of the crop was opening rapidly. Such conditions discolored lint (light spot color grades) and deteriorated lower canopy bolls, resulting in significant shattering and other losses when harvesters eventually moved through the field.

(2) Drought and heat had a profound effect on plant growth and developed as measured by yield and fiber quality, even in irrigated production. Subsoil moisture was limited from the outset, and it is difficult to supply total water needs solely with irrigation. Seed counts were reduced in many bolls. Individual locks should average 6 to 9 seed, but stressed bolls often averaged only 3 to 4 per lock. Many affected bolls included several immature seed per lock. The widespread occurrence of short fiber length (staple) and high micronaire are further indications of the negative influence of weather of cotton productivity.

2000 Season Disease Assessment. (Kemerait) Dry weather was the most serious problem that faced our cotton growers this season; however disease also contributed to the general woe. Based upon samples submitted to the disease clinic here in Tifton and requests for trouble-shooting visits to cotton fields, three diseases were of concern in 2000. These included seedling blight, Fusarium wilt, and Stemphylium leaf spot. There was also a single report of areolate mildew, caused by Ramularia areola, reported by Joel Hudgins in Decatur County. Areolate mildew is not currently of economic importance in Georgia, but is unusual. Joel deserves a lot of credit for both recognizing the disease and then diagnosing the pathogen.

Seedling blight: Seedling blight is known to be more severe on cotton planted when weather conditions are cool and wet, which is NOT what we experienced this year. However, seedling blight was very common in many areas of the state this year. This may be due in part to continual build-up of inoculum in the soil with the peanut-cotton rotations. All of the seedling blight that was evaluated in the clinic and that I saw in the field was the result of Rhizoctonia solani; Pythium seedling blight was not found. In-furrow fungicides that were tested in a study at the Coastal Plain Experiment Station did not increase final yields from the plots that received no treatment at planting.

Fusarium wilt: The disease that was of most concern this year was Fusarium wilt, caused by Fusarium oxysporum f. sp. vasinfectum. The disease was confirmed from several areas in the state, though losses were most severe in Jeff Davis County and surrounding areas. Fusarium wilt was often, but not always, found in association with root knot nematodes. Conversations with pathologists in other states indicate that this problem was not isolated to Georgia. Reasons for this increase in the importance of Fusarium wilt are unclear at the present time, though poor rotations are certainly involved in some instances. The best control of Fusarium wilt integrates crop rotation, nematode control, and the use of cotton varieties with some resistance. Research this winter at the experiment station should help to identify varieties that will be beneficial in Georgia.

Stemphylium leaf spot: Severe outbreaks of this disease were observed in several areas of Georgia and neighboring areas in the panhandle of Florida. The severe cases were associated with rapid defoliation across large portions of the field. The fungal pathogen, Stemphylium sp., appears to infect the foliage of plants that are affected by a potassium deficiency. The best way to manage this leaf spot is to avoid potassium deficiencies.

Variety Distribution of the 2000 Crop. (Brown) Eighty percent of the crop was planted in transgenic varieties as indicated in the table below. Stacked gene (B/RR) and Roundup Ready varieties were the bulk of the acreage, and the two most widely planted varieties were DP 458 B/RR and DP 5690 RR.

The Top 12 Varieties Planted (% of total) in Georgia in 2000, by Technology
B/RR RR B Conventional
DP 458 B/RR - 14.8

DP 655 B/RR - 7.0

SG 125 BR - 3.6

DP 451 B/RR - 3.4

ST 4892 BR - 2.0

DP 5690 RR - 11.1

DP 90 RR - 9.1

DP 5415 RR - 4.9

NuCOTN 35 B - 6.5

NuCOTN 33 B - 4.2

Fiber Max 989 - 3.2

DeltaPine 90 - 2.1

Percent of total by technology group

34.8

31.2

13.3
19.8
USDA Agricultural Marketing Service Survey, September 2000. BXN 47 comprised < 1 percent.

Nematode Management Begins with a Soil Sample. (Davis) The most important step in nematode management is to identify which nematode species are likely to cause damage in a given field. All nematode management decisions depend on that first step, so its importance cannot be over-emphasized. In cotton, as in most row crops, this first step is accomplished primarily through soil sampling, and now is the time to sample to obtain the most meaningful results.

The population levels of all plant-parasitic nematodes are influenced by two factors that change significantly this time of year: the amount of food available to the nematodes and soil temperature. Both factors cause population levels to begin to decline in the fall, so it is critical to sample before levels decline so much that fields with nematode problems cannot be reliably identified.

When cotton plants are defoliated, the amount of food they produce for nematodes is drastically reduced. Nematode population levels may remain steady for a short time, but will soon begin to decline. This is especially true for root-knot nematodes. Nematode eggs are highly durable and will survive until the following spring, so the potential nematode problem is not declining, but the worm-like stages which are identified and counted in soil samples are declining. If the worm-like stages decline too much, we will fail to identify potential nematode problems. The way to prevent this from happening is to sample as soon after defoliation as possible. Sampling before defoliation is even better, though this is impractical for many farmers.

The effect of declining soil temperature is less dramatic than the effect of defoliation because it happens over a longer period of time, but the results are the same. Nematode metabolism, like that of insects, is dependent on external temperatures. As soil temperature declines, all nematode activity eventually stops. When eggs stop hatching and already-hatched nematodes die or enter roots for protection, the apparent population extracted from soil samples declines. When apparent population levels decline below threshold levels, potential problems cannot be identified from soil samples alone.

Many of the soil samples taken from cotton fields are collected by crop consultants, and most crop consultants require that stalks of harvested cotton be mowed prior to sample collection because that allows them to collect samples much more quickly. Farmers can facilitate the earlier collection of samples if they mow cotton stalks as early as possible.

Key points to keep in mind when sampling for nematodes are:

1. Sample before or soon after harvest.
2. Collect soil cores from the crop's root zone, not between rows, because nematodes will be most concentrated near their food source.
3. The most useful samples are collected randomly from an area no larger than 20 acres. Sampling from a smaller area is even better.
4. Collect soil cores to a depth of eight inches from 20-30 different spots within the area being sampled.
5. Mix the soil cores thoroughly and submit about one pint of soil to a diagnostic laboratory.
6. Protect soil samples by sealing them in a plastic bag to keep the sample from becoming dry. Do not use bags designed for soil fertility samples.
7. Do not allow samples to get too warm. Sealed bags sitting in direct sunlight act like miniature greenhouses and heat up quickly.
8. Send samples to a diagnostic laboratory immediately.
9. Don't rely on your memory -- keep written records.

Changes at the UGA Extension Nematology Laboratory. (Davis) Beginning on October 1, the Extension Nematology Laboratory at The University of Georgia began charging fees for specific services. Samples for problem diagnostics, usually referred to as "troubleshooting" samples, submitted through the county Extension office of sample origin will be analyzed at no charge. Samples for purposes other than problem diagnostics, such as planning for next year's nematode management, submitted through the county Extension office of sample origin will be charged $6 per sample. All other samples, including samples submitted from out-of-state and samples NOT submitted through the county Extension office of sample origin, will be charged $25 per sample.

One obvious question is, "What distinguishes troubleshooting samples from other samples?" Troubleshooting samples are taken when a problem has been observed and the county agent is trying to help you determine the cause of the problem. If nematodes could be the cause of the problem, then a troubleshooting sample is justified. Because the goal of troubleshooting samples is to identify the cause of an existing problem in the current crop, troubleshooting samples should be collected prior to harvest.

The way nematode assay results are returned to the county Extension offices also has changed. Counties can now download the results from a special, password-protected site on the Internet that only Georgia's County Agents can access. This reduces the time it takes to get results back to farmers because results are available to County Agents as soon as the samples have been processed. Because the results remain archived on the Internet, County Agents can look up old results anytime there is a need. The form printed off the Internet and returned to farmers now has a statement, based on UGA nematode thresholds, about whether or not the sample indicates a potential nematode problem. The County Agent or an Extension Specialist may provide additional information about specific samples.

Contact your county Extension office for more detailed information on the new laboratory fees or on the new electronic delivery of sample results.

Georgia Ag Statistics Service Conducts Cotton Grower Survey. (Brown) On behalf of USDA and the National Agricultural Statistics Service, the Georgia Ag Statistics Survey has been authorized to conduct a survey of 200 Georgia cotton growers to provide data regarding various production practices, including variety selection, pesticide and fertilizer use, irrigation, and soil and water conservation. The goal is to develop accurate information for such issues as the Food Quality Protection Act so that pending decisions are based on real numbers rather across-the-board assumptions. For example, many pesticide rules and restrictions reflect the idea that each product is used on every acre and at the maximum use rate every time. Data collected from this survey provide much more realistic numbers. Ag Statistics personnel should begin the survey process the fourth week of October.

Calendar

December 13-14, 2000, 2000 Georgia Cotton Production Workshop, Savannah, GA

January 9-13, 2001, 2001 Beltwide Cotton Conferences, Anaheim, CA

Prepared by:

Steven M. Brown, Extension Agronomist-Cotton
Richard F. Davis, Extension Nematologist
Bob Kemerait, Extension Plant Pathologist-Cotton

P. S. Notes

Results from Official Variety Trials will soon be available.

The program for the 2000 Georgia Cotton Production Workshop will be mailed soon.