October 26, 2001 http://commodities.caes.uga.edu/fieldcrops/cotton/
IN THIS ISSUE:
Late Season Defoliation
Cotton Disease Management, 2002
Calendar of Events
Crop Situation. (Brown) As of October 25, about 45 percent of the Georgia crop is harvested. USDA predictions for Georgia have remained at 2.11 million bales from 1.49 million acres, which is an average of 680 lb/A. Perhaps we=ve been biased by the good crop from this region of the state, but we believe our average yield will significantly exceed the USDA projection. Better yields can be attributed primarily to moderate temperatures (we had very few days in excess of 95o F), reasonable rainfall (except for an extended drought in August), and light insect pressure (in most areas). Sporadic cool weather in September and October has slowed the development of late cotton. Last week, many areas had light frost but there was little damage to bolls. Sub-freezing temperatures this weekend may end any progress for late maturing cotton, especially if lows reach 28o F for a couple of hours or more.
Cotton Quality. (Brown) Fiber quality has become a major issue over the past several years. Light spot color grades, high micronaire, short staple, and low uniformity ratio have been costly for Georgia producers. Overall, there are positives in color and micronaire but negatives with staple and uniformity.
To date, color grades have been quite good. Better than 90 percent of our crop is 41 color grade or better. The primary cause of reduced color grades is weathering. Though we have had significant rains this fall, fronts have moved through quickly and then skies have cleared, allowing cotton to dry and brighten. Less than 6 percent is high mic (in excess of 4.9). High mic is most often associated with drought and high temperatures. These stresses cause boll shed and a concentration of carbohydrate production in fewer sites, resulting in greater cellulose deposition per individual fiber and higher micronaire.
Over 30 percent of the classed samples are short staple. Similarly, uniformity figures for the Macon Classing Office are 80.7 compared to 82.0 for the Memphis Office. We hope our numbers will improve as the season progresses. Short staple and low uniformity ratio may be related to genetics and fruit production zone. On the latter point, the success of boll weevil eradication allows us to make bolls in the upper plant canopy, a zone that may have a tendency for shorter fibers. Short staple creates problems with spinning and is thus in serious disfavor with mills.
Late Season Defoliation. (Brown) The time has come to GET THE CROP OUT. Cool temperatures have arrested boll maturity, so it is questionable how many more top bolls we can expect to mature. We probably will not open and fluff many bolls with significant stink bug damage. Most fields will benefit from an aggressive rate of boll opener (Cotton Quik @ 2 qt/A; ethephon @ 2-2.6 pt/A; or Finish @ 1.5 pt/A) and a standard defoliant (DEF/Folex, Ginstar, Harvade, or Aim). The only fields to gamble with and not spray are those that currently have few open bolls. There is some chance that a freeze is not imminent and that these fields may yet survive and progress.
Cotton Disease Management, 2002: It=s not too early to begin preparations now. (Kemerait) During the 2001 season, most cotton disease problems, such as seedling disease and Fusarium wilt, have been minor across the state; however, individual growers have suffered significant yield losses from boll rot and nematode damage. Substantial boll rot appeared in some fields where dense growth occurred from excessive nitrogen fertilization and/or inadequate control of plant height with growth regulators. Also, an interesting boll rot, apparently caused by the fungus Colletotrichum, appeared in several southwest counties earlier in the season. This rot began with deep, sunken lesions on the boll that produced copious spores and eventually engulfed the entire fruit (Figure 1). Unlike more common boll rots, where the pathogen infects after the boll is damaged by insects or as the boll begins to open, Colletotrichum is able to produce its own wound, known as anthracnose (NOT related to anthrax--some folks have confused the two). This boll rot seemed to be confined to a specific region in the state and was most likely associated with early season weather patterns, such as tropical storms.
Disease preparations for 2002: Growers who have had troubles with seedling disease in the past may want to consider using fungicides in the hopper box or in the furrow at planting next season. Granular and liquid in-furrow formulations have been effective at reducing seedling diseases in some instances in Georgia. Obviously, cooler and wetter conditions at planting can make seedling disease worse, but this is most often true if the field has a history of seedling disease. Cool temperatures alone have much less impact on seedling disease. Growers who have had a problem with Fusarium wilt this season should consider rotating the troubled field out of cotton and also providing control of parasitic nematodes. Successful management of boll rot next season will depend on the weather and the reduction of rank vegetative growth.
Nematodes: Damage from parasitic nematodes has caused problems for growers and researchers across the state this season. In some cases, growers were unaware that they had a problem with nematodes until this season; perhaps because they were finally able to compare Agood cotton@ with Asorry cotton@. Severe yield losses were observed in fields infested with root knot nematodes, reniform nematodes, and in several cases, sting nematodes. In most cases, nematode populations have been able to build in a field due to poor rotation. Figure 2 was taken by Tommy Cummings in a field in Jefferson County that was severely affected by root knot nematode. Note that the plants in the foreground appear to have been killed by the nematodes; in fact the nematode pressure caused them to Acut-out@ prematurely.
Nematode preparations for 2002: Growers who are concerned about nematode populations in their fields should be collecting soil samples for analysis now. If they wait until later in the year, the ability of the diagnostic lab to find nematodes is reduced because 1) eggs that are present are not identified, and 2) many parasitic nematodes that remain in the soil will travel to greater depths and will not be included in the sample. If a grower is submitting samples to diagnose a problem from this season, they are considered Atrouble shooting@ and no charge will be applied. However, even though a charge may be applied for other samples, the results will be well worth the investment. From these results, the grower will be able to determine IF he has a nematode problem and what types of nematodes are in the field. Knowing the type of nematode will help the grower determine suitable winter cover crops and also rotational crops for the next season. For example, a cotton grower with root-knot nematode problems would not want to plant corn or sorghum in rotation with cotton; however a grower whose fields are infested with reniform nematodes could rotate his fields with either crop. Growers who have had a problem with nematodes this season should consider crop rotation or the use of nematicides for next season. They may wish to map their fields now in order to know where the Ahot spots@ are for the following season. The benefits of pulling stalks in the field at the end of the season for nematode management is not likely to be worth the cost or effort. Deep turning the field at the end of the season will also not affect the nematode populations.
For further information on disease and nematode control in cotton, please do not hesitate to contact me.
Calendar of Events:
December 11 & 12, 2001 - Cotton Production Workshop ‑ RDC, Tifton, GA
January 8‑12, 2002 - 2002 Beltwide Cotton Conference ‑ Atlanta, GA
Steven M. Brown, Extension Agronomist-Cotton
Bob Kemerait, Extension Plant Pathologist
Putting knowledge to work
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WARNELL SCHOOL OF FOREST RESOURCES, COLLEGE OF VETERINARY SCIENCES
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