Cotton Defoliation for All Situations

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Virtually all Extension Cotton Specialist readily relay that  there is no preferred defoliant material and/or tank mix that is always preferred. There is no such thing because the choice of products will depend upon past weather, crop stage, juvenile growth, percent of open bolls, anticipated harvest date,  the weather 1-2 days prior to application, the weather the day of application, projected weather forecast 2-5 days after application, when the crop was planted, and how it was fertilized. All products have a unique purpose that must be considered when evaluating these factors.

Complicating the choice is the fact that sales of defoliants may be promoted as “new products”. There are no products that have a new active ingredient. Rather any “new product” is simply some combinations of older products or older products with new surfactants or additives. As such, one needs to evaluate what is needed to defoliate and then select a product that fits.

The most expensive treatment of a three-way tank mix with products that include hormonal activity, herbicidal activity, and boll opening products will work in just about any situation. However, this is usually the most expensive combination. Too, even such a tank mix will often mandate to alter rates depending upon climatic conditions.

Rather than choosing the most expensive route, consider some of the pointers below.

  1. Cotton fields that complete flowering (cut out) 100% early will likely need to be treated differently than fields still blooming in September. Those still blooming are likely to still setting bolls and that will require more time to mature. Fields that cut out 100% will likely have more mature bolls and could be defoliated sooner but are more likely to develop new growth.
  2. Lacking any major sinks of energy (large leaves and efforts to set or mature bolls), the plant will concentrate efforts to produce new leaves quickly.
  3. Using the Nodes Above Cracked Boll (NACB) method will generally provide a safe time to defoliate a crop as long as there are not missing fruiting positions. If missing first fruiting positions exists, then one must examine the seed coat for maturing to make decisions on timing of application.
  4. Generally August 25th is considered the last date to set a harvestable boll within North Carolina. However, for cotton within Eastern NC, this date is more likely to be extended as late as September 1st, and even later in some years. Even so, earlier harvest should be the goal to reduce weight and quality loss of the bottom, open bolls.
  5. There is no need to utilize higher priced products promoting faster bolls opening or quicker defoliation if one does not intend to harvest 3-4 days earlier than one would anticipate from using other cheaper products not quite as efficient. However, products that open bolls more quickly may be warranted later in the season should cold weather threaten to negatively impact normal boll opening and defoliation process.
  6. Equally, if not of greater importance than product, is the volume of water, pressure and nozzle selection. Aim for at least 20 GPA and high pressure with flat or twin-fan nozzles  (Note:  With some sprayer of very high pressure, 15 GPA has been sufficient. However, this also depends upon the number of bolls that need to be opened as well as a crop without a rank canopy of leaves. Simply be aware and aim for at least 20 GPA). Hollow-cone nozzles can be used but slow the speed of the sprayer to allow penetration of the spray patter into the canopy. Do not use air-induced nozzle (AI or TTI nozzles).
  7. Aim, Blizzard, Def, Folex, ET, Harvade, Display, Resource, Harvade, and QuickPick are herbicidal defoliants and tend to injure the plant causing the plant to produce ethylene and thus, leaf abscission and/or boll opening. These products can dry or kill leaves if applied at too high a rate during times the temperature is high. Conversely, higher rates are necessary when temperature are colder.
  8. Dropp, FreeFall, Klean-Pik, Finish, Terminate, CottonQuik, FirstPick and Prep are hormonal defoliants that increase ethylene production. Because they are hormonal, they are less likely to cause leaf stick during warmer temperature but some may be much slower or ineffective during cold weather.
  9. Thidiazuron (TDZ) products such as Dropp, FreeFall, Klean-Pik, Ginstar, Adios, Cutout, Redi-Pik and similar generic products are defoliants that also prevent basal and terminal regrowth. However, Harvade is also noted to prevent terminal regrowth.
  10. Even when boll opening is not desired, the addition of Prep or similar generic product at low rates (6-10 oz/ac) usually enhances defoliation.
  11. Use of surfactants will generally reduce rain-free period about half the label recommendation. It will also aid in tank clean-out. However, do NOT add adjuvants other than those listed on the label for Ginstar, Adios, Cutout, Redi-Pik or similar generics.
  12. Adding AMS to TDZ products when applied during cloudy weather will enhance these products.
  13. Accelerate can be added to Def/Folex and will increase leaf drop by about 25% during the first few days. However, comparisons of leaf drop to this product applied alone  to the same rate with Accelerate will be the same near day 7-10 day.
  14. CottonQuik, Frist Pick and similar generic products are effective products that can be applied when temperatures get low (40-60 degrees F). They work well in warmer weather too. Simply realize that tank mixes and lower rates are normally preferred during warmer weather. If used, realize these products can be corrosive to nozzles. Be prepared to clean the nozzles and tank. Aim to avoid storing these products overnight within tanks and hoses.
  15. Many products can etch glass and/or damage metals. Avoid drift to homes, cars or other property.
  16. Defoliating drought-stressed cotton can be difficult since the leaves are often thicker and more leathery than normal. Other than TDZ products, avoid high rates of other products. Addition of silicone surfactant often increase defoliant effectiveness.

As mentioned earlier, which product chosen to apply alone or as a tank mix will depend upon many factors. The most recent data is provided within the Cotton Information publication. Information within this publication provides crop growth stage scenarios and temperature ranges listed with appropriate products, tank mixes and rates.