Alabama Cotton Picksack

• Alabama Crop Update............... D. Monks, C. Burmester, D. Delaney
• When to Begin Defoliation........ D. Monks, C. Burmester, D. Delaney
• New Cotton Harvest Aids........... M. Patterson
• Harvest Aid Performance.......... M. Patterson, C. Burmester, D. Monks
• Check Cotton Roots Now............W. Gazaway
• 1997 Cotton Calendar................. D. Monks, D. Delaney

Unfortunately for many southern counties, rainfall that was needed during the critical bloom and early boll development stages did not fall throughout most of August. Cotton shed most of the small bolls and squares that were on the plants in order to mature the earlier set crop. Many fields were wilting severely by mid-day. This probably results from a combination of poor root development in the early summer and very dry conditions over the past several weeks. Fields in the sandy coastal plain areas generally need rainfall on a weekly basis to maintain soil moisture. Irrigated fields should yield well, especially where stinkbugs were controlled late in the summer.

The hot weather in late August has helped to mature the late cotton crop in northern counties. The dry weather has also been a problem for late-maturing cotton and soybeans. Producers that destroyed cotton in July and early August were preparing land, killing bermudagrass, and working on eroded areas.

For current information on crop condition, weather (ie. DD60’s), production recommendations, and local cotton news, check our site on the Internet at:

http://www.aces.edu/department/cotton/index.html

This is the time of year when producers must decide when to terminate the crop and begin picking. Cotton bolls that are open can lose weight and quality can decrease due to yellowing or spots, especially under wet conditions. Open bolls can deteriorate under wet conditions over several weeks such that the locks will fall out of the bur. Cotton that is defoliated early but not picked for several weeks may also be more vulnerable to storms (for example, hurricanes). There are several ways to determine when a boll is mature enough to open and harvest without affecting yield and quality.

The first method is to cut open the last boll you expect to harvest. When mature, it should be hard to slice in cross-section with a sharp knife. The seed coats should be light brown to tan in color. Inside the seed there should be no gelatinous material.

The second method is called Nodes Above Cracked Boll. Find the uppermost first position boll that is cracked. Count the nodes above it to the last boll you expect to harvest. The nodes that are 4 or less above that position should be mature. If nodes are 5, depending on how bolls were set, the crop may still be mature. If the nodes above cracked boll number 6 or greater, harvest aid application will likely result in yield and quality reductions.

The third test is to count the open bolls and green bolls you expect to harvest. If percent open bolls is 60 or greater, harvest aids can be applied. Note: this test can cause premature harvest aid application if there is a large fruiting gap in the cotton plant.

When trying to determine how long it takes for each position to mature, remember that cotton fruits in 3-day increments upwards and 6-day increments out the same branch. Therefore, each node may require 3-4 days to open when counting upward towards the terminal. These intervals can be longer under cool, wet conditions or shorter under dry, warm conditions.

Finish from Rhone-Poulenc, CottonQuik from Griffin, Dropp Ultra from AgrEvo, and additional ethephon (Prep) products including Boll'd from Terra and SuperBoll from Griffin will be sold in Alabama this year. How will these products be used in a harvest aid program and are they better than the old products we have been using?

Finish is being sold as a stand alone product which will defoliate, open bolls, and provide regrowth control, and when used at the 3 pint/acre rate it has looked good in our research trials. Adding some Dropp to Finish used at the 2 pint rate will provide more regrowth control and adding Def/Folex in cooler weather will provide more consistency under these conditions. CottonQuik will benefit from the addition of Dropp. Rates for CottonQuik range from 1.75 to 3 quarts/acre. Dropp 50W at one pound to 10 acres added to the low rate of CottonQuik will provide better overall defoliation and regrowth control. CottonQuik will also open bolls. Dropp Ultra is a mixture of Dropp and diuron. The activity of Dropp Ultra in cool weather is improved over Dropp by itself. This product will provide good defoliation and regrowth control in early to mid fall and can be mixed with a boll opener if needed. As temperatures decrease in October then the addition of Def or Folex to Dropp or Dropp Ultra will help. The new ethephon formulations work essentially like Prep and should be used at the same rate out of the jug.

A good harvest aid treatment should defoliate the crop, open bolls if needed, and prevent regrowth if you cannot pick within 14 days from treatment. Traditionally mixtures such as Def/Folex + Dropp + Prep and Harvade + Dropp + Prep have provided all the qualities mentioned above. The economics of newer products should be compared to our standard treatments when considering their use.

Five years of research evaluating harvest aids for performance and effects on fiber quality revealed that all treatments increased defoliation above the untreated check (see attached tables). The data provided are based on a "Performance Index" rating that includes defoliation, leaf stick, regrowth, and overall performance. The LSD figure at the bottom of each table designates the "Least Significant Difference" statistically and should be used to compare between two treatments. For example, if Treatment 1 = 70 and Treatment 2= 50 and the LSD= 10 then the treatments are considered different because the difference (20) is greater than the LSD (10). If the LSD value had been 30, then they would not be different (70-50= 20 and 20 is less than 30). Fiber quality was generally not affected by any harvest aid treatment (data not attached). Percent of open bolls was increased by harvest aid treatments containing Prep (ethephon) at 7 and 14 days after treatment compared to the untreated and also compared to treatments not containing Prep. High terminal regrowth was more related to environmental and crop conditions than to harvest aid treatment, and was a serious problem only in one year (1995) when late-season rainfall followed a summer drought. Basal regrowth was common all years except 1994 when good growing conditions allowed the crop to deplete the applied fertilizer and use soil moisture for optimum growth. Treatments containing Dropp or Roundup were most effective in reducing regrowth. Desiccation from harvest-aid treatments was rare except in 1994 when all treatments caused some desiccation at 7 days after treatment. A Dropp + Prep mixture provided the numerically highest overall performance index of any treatment during the 5 year period. Total lint yields were generally equal for all treatments.

Now is a good time to check your cotton plant roots. The condition of the roots at this point in the season can indicate a lot about the past season and warn of future problems. For example, poorly developed roots can mean the presence of a hard pan, acid soil, high water table, seedling disease, or nematodes. Plants with shallow or underdeveloped root systems often exhibit stunting, nutrient deficiency, wilts, and other disorders during dry periods or other unfavorable growing conditions.

Look for stunted plants or plants that are off-color and exhibit apparent nutritional deficiencies. Carefully dig the plant, leaving a large portion around the roots intact. Do not pull the plant because the vast majority of the roots will be left in the soil. If the soil is loose and moist, carefully remove the soil from around the roots. If not, carefully soak the soil off with water and examine the small secondary roots. If root-knot (RK) nematodes are present, affected roots will contain numerous small swellings and galls. Beware: cotton roots do not show root-knot nematode damage as readily as tomato, okra, or peanut. The presence of tiny galls on the roots could mean cotton has been badly damaged by RK nematodes. Reniform nematodes cannot be detected as easily, so nematode soil samples must be analyzed for their presence.

Why go to the trouble of looking a roots when soil samples are easier to collect? If you find RK galls on cotton roots, there is no need for a nematode soil sample. The presence of RK nematode galls on cotton roots are a positive indication that it is in the field since no other root-knot species are known to feed on cotton roots.

Now is the best time to sample for nematodes in cotton fields. Nematode populations peak in late August and September. Soil samples should be taken only from fields suspected of having RK nematodes and should not contain fresh roots. Do not forget to provide the field's cropping history when sending in nematode soil samples.

Alabama Cotton Picksack Newsletter Reference: PSK-10-97; D. Monks and C. Burmester, Editors

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