Monday, May 20, 2024

Defoliation trials, thoughts and concoctions for the next few days

• By Tyson Raper •

defoliating cotton
A rig applies defoliant to a Tennessee cotton field — photo courtesy University of Tennessee

I dug through my closet to get a jacket this morning. With cooler temps creeping into the forecast, calls on defoliation timing, products and rates have really picked up. In this blog, I highlight results from the earliest defoliation strip trial we’ve applied in 2021, share a few concoctions that I’ll be running on the earliest cotton here in Jackson next week, circle back on boll maturity and give a couple of additional thoughts on what we will likely face in the coming weeks.

Lake County defoliation demo

Last Thursday (Sept. 16) we applied a strip defoliation demo adjacent Reelfoot Lake in Lake Co, Tennessee. I returned to Lake County to rate and fly the trial Sept. 21. To learn more about the demo and the results, click the image below or play the 3-minute video above. All treatments, with the exception of the untreated, included a 16-ounce application of Finish.

What is in the tank moving into next week?

First, let me say that almost everything I’ve walked is two shot. Lows should slowly climb out of the 40s, through the 50s and back to the low 60s by Monday of next week. Still, the only three days that might deliver “decent’” thidiazuron activity are next Monday, Tuesday and Wednesday (9/27, 9/28, and 9/29). After that, we move back into the upper 50s at night with sub-80 degree Fahrenheit highs.

My first shot concoction moving into next week is 6-8 oz Folex plus 8-12 oz Finish plus 8-12 oz Prep. As temps climb, I’ll slowly back down from 8 oz Folex to 6 oz. Based on the amount of juvenile leaves on these plants, my second shot will follow 7-10 days after the first and will consist of a PPO plus all the boll opener that remains on the label.

Aim at 0.75 oz plus 0.25% NIS OR ET at 1.5 oz plus 0.5% COC will likely be my rate if temps hold in mid 50s and max temps remain below 80.

Your other first-shot option is Ginstar. Remember that there are two actives in Ginstar — the first is thidiazuron and the second is diuron. Again, thidiazuron is not going to provide activity at our current temperatures — activity will only be notable for a few days next week.

Diuron will be carrying the weight. Rates are going to have to be hot — somewhere between 5 and 7 oz. If you can hit rate, you will have a better chance at removing juvenile leaves than the preferred mix I described above. But if you miss rate . . . you know the deal.

When do I start on green acres?

We are still 14 days away from Oct. 6, and there are a large number of sunny days in the forecast between now and then. Even with cool temperatures, expect bolls to continue to mature- just slowly.

And remember — the survey says — if you decide to the pull the trigger in the next few days on bolls that still have a good bit of jelly in the seed, there is a good chance they will not open. With that said, by Oct. 6, my decision to make an application will be based on the forecast and not the crop.

What about ‘preconditioning’?

I’ve visited with a few over the past week that mentioned “preconditioning.” I am not a fan of the term nor the practice. Actively growing, healthy cotton plants mature bolls.

Boll maturity requires translocation of photosynthate from leaves. The most important leaves to maturing uppermost bolls are at the top of the plant and those are the ones you will damage if you attempt to precondition. Injuring these leaves will drastically reduce the amount of photosynthate available to those developing bolls and either completely slow or halt boll maturity — costing both yield and quality.

Don’t precondition. Instead, trigger your first defoliation application either

1) when the uppermost boll is mature or

2) the forecast indicates it is time to go. The intent for any harvest aid application, in my opinion, is to remove as many leaves as possible and open as many bolls as possible.

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

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