UGA Georgia Cotton Newsletter
August 14, 2002 - Click here for a printable copy
In this issue
Growers Likely to Begin Seeing Damage From Nematodes and Boll Rot in August
Thoughts on Defoliation
Folex Acquired by AMVAC Chemical Company
Crop Situation. (Brown) The Boll Weevil Eradication Program certified 2002 Georgia cotton plantings at 1,439,887acres , slightly below the rounded figure of 1.5 million acres USDA estimated. Overall crop conditions are highly variable because of limited initial subsoil moisture and the lack of widespread rainfall. (Click Here for a map showing the Boll Weevil Eradication Program Certified Acres by County.) As of August 12, the Georgia Agricultural Statistics Service rated the crop as 47 percent good to excellent. Portions of the state are extremely drought stricken, and many non-irrigated fields are 2 to 3 weeks past hope of rescue. Over the past 10 days, numerous dryland fields have lost considerable prospects, and yet there are pockets of exceptional cotton. Can we finish with anything close to an average yield of 629 lb/A? The initial USDA production estimate as of August 1 projected Georgia yield at 738 lb/A, which seems extremely optimistic (if not downright unrealistic) from here.
Worm pressure has been significantly greater than since Bt cotton was introduced, but many would consider the current situation more "normal" than what we've seen since 1995. A grower from Randolph County recently commented, "This level of worm pressure, what we've experienced in 2002 will force a lot of producers to rethink Bt cotton."
Growers Likely to Begin Seeing Damage From Nematodes and Boll Rot in August. (Kemerait) In the past several weeks, rainfall has been common, and in some areas abundant, over much of the Coastal Plain. For the most part, this is welcomed news as the rain will help the cotton growers achieve greater yields. However, abundant rainfall will also create the perfect environment for the development of boll rot, especially in fields where a) the bolls have been damaged by insects, b) rank growth is common (perhaps through the use of excessive nitrogen), and c) the bolls are approaching maturity. Insect damage can create entry points for fungal and bacterial pathogens that can destroy the young lint; rank growth, coupled with rain, creates a zone of high humidity within the canopy that promotes boll rot; and as the bolls approach maturity and begin to open, they are very easily invaded by boll rot pathogens. Thus, rainfall not only increases humidity around the bolls, but also acts as the vehicle to wash pathogens into the developing boll. It would be unlikely for some of these pathogens to enter the boll if no wounds or open sutures were present.
So, the question now is what can the grower do at this stage of boll formation to minimize further boll rot. Research has shown that the use of fungicides to control boll rot is generally ineffective. The use of mepiquat chloride (Pix) reduces rank growth and may reduce the humidity within the canopy, thus reducing conditions favorable for boll rot. Timely defoliation and harvesting can also be very beneficial to prevent weather deterioration of seed cotton.
Nematode Damage - Growers are most likely to begin to observe damage from nematodes, such as southern root-knot, reniform, and Columbia lance, as the cotton plants enter reproductive growth stages and bolls begin to form and develop. The additional stresses associated with reproductive growth, coupled with damage to the root systems caused by parasitic nematodes, often cause the afflicted plants to be stunted, appear chlorotic, and perhaps to "cut-out" prematurely. These same symptoms may be caused by other factors, such as poor fertility; therefore, the grower should take soil samples from symptomatic areas to confirm the presence of the nematodes. It is often useful to pull separate samples from both afflicted and healthy areas of the same field to compare the size of nematode populations.
By this time of the season, there is little that can be done to minimize the impact of the nematodes if they are severe in a field. Recent rainfall will allow damaged root systems to provide more water to the plant and may reduce the severity of symptoms that would otherwise appear. Several growers across the state have already noted "weak" areas in their fields and have been surprised to find that reniform nematodes, previously unknown on their farms, have reached very damaging levels. Knowing which nematodes are affecting cotton in their fields will help growers make management decisions (suitable rotation crops and use of nematicides) for the 2003 season.
Nematode Round-Up, 2002 - Just a reminder to county agents that a cotton nematode survey for 2002 will be conducted across the state from late August through early November. Such a survey is important to better understand the distribution of parasitic nematodes within the cotton production areas of the state and should allow us to generate more detailed maps on a county-by-county basis. Watch for further details to appear shortly.
Thoughts on Defoliation (Jost) (Also submitted to the "Specialist Speaking" column of Cotton Farming Magazine.) As rainfall appears to be drying up fields are rapidly approaching the time for defoliation. As far as the time to defoliate there are several techniques that can be utilized. Counting nodes above cracked boll (NACB) when the plants have a uniform fruit distribution is one technique. Determining the percentage of open bolls is another along with the "sharp-knife" technique. Generally, once the average NACB reaches 4 or the field is greater than 60 to 70% open it is safe to proceed. Harvest-aids can also be applied when all bolls cut with a sharp knife reveal seeds without any gelatinous material.
Every year it is somewhat of a guessing game as to which product to use, as there are several available. It is also not uncommon for one product to work well one year and be a near failure the next. Research across the cotton belt has shown that tank mixtures of differing modes of action provide the most consistent response.
Each harvest aid can be classified as to having one of two modes of action, herbicidal or hormonal. A tank-mix consisting of both of these modes of action increase the chances of success. Herbicidal defoliants include, Def, Folex, and Aim. Hormonal type defoliants include Dropp, Leafless, Finish, Harvade, and Ginstar. Also included in the hormonal type harvest aids are the boll openers Prep, CottonQuik and other ethephon containing materials.
Click Here for the 2002 Harvest Aid Recommendations.
Folex Acquired by AMVAC Chemical Company. (Brown and Jost) Recently the harvest aid Folex 6EC has been acquired by AMVAC Chemical Company from Aventis Crop Science. It is scheduled to be on the market within the next couple of weeks.
Reminder - The South Georgia Cotton Breeder Tour is coming up. It will be held on August 27.
Philip H. Jost, Extension Agronomist-Cotton & Ag Crops
Steven M. Brown, Extension Agronomist-Cotton
Philip H. Jost, Extension Agronomist-Cotton & Ag Crops
Bob Kemerait, Extension Plant Pathologist
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