Thursday, May 30, 2024

Defoliating in volatile weather conditions (is this the end of October?)

• By Tyson Raper •

University of Tennessee cotton defoliation trials — photo courtesy UT

If you trust the forecast, volatile temperatures should increase over the weekend before again falling into the upper 40s by the middle of next week. Thanks, 2020.

Unfortunately, we do not have great options after Sunday and fields in West Tennessee are wet. This blog covers the mixes I’m running prior to Saturday afternoon, Sunday through mid-week and thoughts on whether or not that green, soft boll will mature before a freeze.

For those that can run tomorrow or Saturday, my go-to mix would be:

2-3.2 oz Thidiazuron (Dropp, Daze, Takedown) plus 4-6 oz tribufos (Def, Folex) plus 16-32 oz ethephon

I like products with ethephon + cyclanilide (Finish, Terminate). If you decide to run Finish, I’d blend 12-16 oz Finish with another straight 6 lb ethephon product at 12-16 oz. Blend more ethephon in if more boll opening is needed OR if you plan to run a single shot. If most of your bolls are open, definitely drop ethephon rate considerably.

I’d stop running this mix Sunday — I want a minimum of two good days of warm temps with this blend. If applying Sunday, you won’t even have 24 hours Sunday I’d be looking into another concoction (see below).

Be ready to come back. Even the best 1 shot concoctions have been turning into two shots this year- we just have too much leaf on each plant to get away with a single application. And if you are trying to convince an immature boll to open, I’d rather you give me two 16 oz applications of ethephon than one 32 oz application of ethephon.

For those that are looking at Sunday-Wednesday of next week:

6-8 oz tribufos (Def, Folex) plus 16-32 oz ethephon

This will likely be a swing and a miss on juvenile growth- which is fine, in my opinion, because I’m going to follow this first shot with a second shot of a PPO (Aim, ET, Sharpen, ETC). If you have an area that doesn’t have juvenile growth, you might just get by with a single shot of Folex and ethephon.

A few will likely stretch a thidiazuron + diuron product (Ginstar, Cutout, Adios) down into these temperatures. If the forecast is accurate, next week will be below ideal temperatures for those products and I do not like running them in volatile conditions. That said, If you decide to run Ginstar next week, I’d look at rates between 4-7 oz. I’ve got strips of Ginstar and Ginstar + Folex in my defoliation strip trial at Gift that we applied last week and both are working but leaf shed isn’t yet complete.

A few will run PPOs in the first shot. This can be a very cheap concoction, but it is also risky. These products create severe leaf injury quickly and if you miss rate or run too hot of an adjuvant you will stick leaves. In my opinion, I would hold the PPOs until we get into the second shot. . . or until temperatures get extremely cold.

How many heat units does it take to mature a boll? What is a heat unit, anyway? Do we mature bolls when night temperatures are below 60? 55? 45? Unfortunately, we have a considerable amount of late cotton.

I’m hopeful we will be able to pick the majority of the bolls present on these plants, but there will definitely be some left behind on the latest planted cotton.

I’ve been suggesting all week that sunlight alone helps mature bolls at temperatures greater than 50 degrees Fahrenheit. We watched several fields open up this past weekend.

Dr. Tyson Raper is University of Tennessee Extension and small grains specialist. He may be reached at

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