How Do We Manage Defoliation for the Rest of This Season? (Collins & Edmisten)

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We’ve received a lot of phone calls over the last few days about how to address various cotton defoliation issues for the remainder of this season. Below are the most common scenarios for which we have been called and how they could be addressed:

Scenario 1: I haven’t defoliated yet, I have a lot of bolls that need opening, but boll opening has been very slow. What can I do?

Typically we would say to wait, especially if this was September or early October. Warm sunny weather with decent soil moisture is the best promoter of boll maturity. However, generally speaking, once we reach mid October, is pays less and less to wait on bolls to mature and open at the expense of a decent bottom crop. With that said, we encourage growers in every year to evaluate and closely watch their local weather forecasts in hopes that warm sunny weather may continue beyond mid October to further develop upper unopened bolls, especially in later-planted cotton where unopened bolls may contribute more to yield than normal. Unfortunately, based on the current forecast for most areas of NC as of today (10/17/2017), we are entering a cool spell for a while, especially at night. Boll development will very likely slow down to a negligible rate at this point, therefore we cannot in good faith say that waiting on bolls to mature beyond this week will realistically accomplish anything. Warmer weather is predicted towards the end of this week and weekend, which may provide the last decent opportunity to defoliate with the best odds of opening some bolls that are on the verge of maturity. Side note: If a frost is eminent, do something at least 3 to 4 days ahead of the frost if possible, ideally on a warm sunny day (see other scenarios below).

So what are your options in regards to product selection? There is no product that can accelerate maturity of immature bolls that are high in moisture content and seed development is poor. However we can promote or accelerate opening of bolls on the verge of maturity. In your defoliant tank-mix, it may be best to use the maximum rate of ethephon according to the label (2.667 pints/A of products containing 6 lbs a.i. per gallon in any combination. The maximum rate of ethephon that can be applied in a season is 2 lbs a.i. per acre in any form or combination).

  1. For regular ethephon products containing 6 lbs a.i. per gallon (products such as Prep, Super Boll, Ethephon 6, several other generics), use 2.667 pints/A when tankmixed with products such as Folex and TDZ, or when tankmixed with a TDZ+diuron product (Ginstar, Adios, Cutout, other generics). A TDZ+diuron product may be preferred over regular TDZ (Dropp, Freefall, etc) at this point….see other scenarios below.
  2. Finish or Terminate: Use 2.667 pints/A –OR- 1 quart/A and add 10.6 oz/A of regular ethephon (Prep, Super Boll, Ethephon 6, several other generics) to reach the maximum amount of ethephon allowed. Finish or Terminate should not be used alone. The addition of another product such as TDZ+diuron would likely improve overall defoliation, especially if regrowth is present.
  3. CottonQuik or FirstPick: Use 2 quart/A. These products are known to be corrosive and can clog lines and tips, and aren’t used much anymore. However, in cool or cold weather, these products are very effective at opening bolls. The addition of other defoliants may be necessary for overall defoliation, depending on the fields needs.

 

Scenario 2: I have already defoliated and used ethephon, but these bolls still will not open. It looks like a frost is coming…..What can I do?

There is a chance that some folks may encounter a light frost tonight in some spotty low-lying areas, if there is little wind. There’s not much we can do about that now, but chances are, this frost will likely be very light if any at all. A light frost can sometimes help open bolls. We don’t always have the luxury of clear, advanced notice of a frost, however, if we do, you need to try to do something at the very least 3 to 4 days ahead of a frost, ideally on a sunny warm day. Unclear or constantly changing weather forecasts make these decisions difficult. If you did not use the maximum amount of ethephon allowed when you first defoliated, you could apply the remainder labeled amount as long as it is not a negligible amount. For example, if you used 1.5 pints per acre of ethephon (6 lbs a.i. per gallon) when you first defoliated, then you could now apply the remaining 1.167 pints/A. If you used more than 2 pints/A of ethephon when you first defoliated, the remaining allowed amount may be negligible and will not likely have much additional effect.

So you used a high rate of ethephon the first time you defoliated and a frost is eminent 3 to 4 days from now. One last option is using paraquat (3 lbs a.i. per gallon) at 8 to 11 oz/A. This does not always work, and may only work on bolls that are on the verge of maturity. If applied on a sunny and warm, dry day, it could help dry out the carpal walls to stimulate bolls to barely pop open, so that when the frost occurs, the burs would retract and open the boll versus freezing shut. Paraquat could be applied with the remaining allowed amount of ethephon. However, use this practice is a last resort. This approach can be inconsistent in regard to boll opening and will likely stick leaves if used as a first attempt.

Scenario 3: I haven’t defoliated yet and I have a lot of regrowth…Should I stick with TDZ or switch products?

In most years, we experience a gradual decline in temperatures, perhaps with moderately warm days and increasingly cooler nights. In most years, it can be difficult to know when we should discontinue the use of TDZ (Dropp, Freefall, other generics) and switch to a TDZ+diuron product (Ginstar, Adios, Cutout, other generics). This year, we have somewhat of a clear concise break in time, and that time is today. Regrowth will likely subside and be less of an issue from now on due to cooler weather, however many fields already have a large amount of regrowth already present. From this point forward, it is likely better to use a TDZ+diuron product to address regrowth issues and for overall defoliation when regrowth is present. If using TDZ+diuron and ethephon as your sole tank-mix, the rate of TDZ+diuron should be no less than 8 oz/A (warmer weather) and more commonly 10 oz/A. Higher rates (12 oz/A) may be justified in very cool temperatures. If you are using Finish or Terminate tankmixed with TDZ+diuron, the rate of TDZ+diuron should be 6 to 8 oz/A (use the lower rate if temperatures are warm).

Scenario 4: I have already defoliated, got delayed with harvest, my bolls are open but now I have a lot of regrowth…what should I do?

It depends. The most agronomically appropriate approach would be to use a TDZ+diuron product alone at 10-12 oz/A (if temperatures warm up, you could decrease this to 8 oz/A). This is an added expense and will require more time to work, but it is effective and may be appropriate if there is a lot of regrowth to the point of the field appearing that it hadn’t been defoliated due to significant regrowth. Coverage is very important as regrowth is often compact and it can be difficult to get coverage of the regrowth in the lower canopy. If regrowth isn’t severe, you could pick through it and have it ginned rather quickly. Some gins have stated that it is easier to remove green tissue from lint versus dried dead leaf tissue. That is beyond our area of expertise so consult with your gin before making these decisions, however regrowth is high in moisture and can also stain lint, so it is important to gin it quickly if you decide to pick through it. Another option, again as a last resort, is to use paraquat at the rates mentioned in a previous section. However it is important to note that paraquat can lead to desiccation of leaves which can negatively impact grades. This option is only recommended if you intend to harvest it quickly (at least 3 days after application according to label) in hopes that it will collapse regrowth before it completely dries or desiccates to minimize the amount of green material entering the picker.

Written By

Dr. Guy CollinsExtension Cotton Specialist (252) 578-7719 guy_collins@ncsu.eduCrop and Soil Sciences - NC State University

Contributing Specialist

Photo of Dr. Keith EdmistenDr. Keith EdmistenProfessor of Crop Science & Extension Cotton Specialist (919) 515-4069 keith_edmisten@ncsu.eduCrop and Soil Sciences - NC State University
Posted on Oct 17, 2017
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