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Defoliating In Volatile Weather Conditions (Is This The End Of October?)
DR. TYSON RAPER
JACKSON, TENN.
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 hrs. 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 2 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 does a heat unit REALLY mean, anyway? Do we mature bolls when night temperatures are below 60? 55? 45? I’ve been discussing these questions with colleagues for the past two weeks. Unfortunately, TN has 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. I’ve been suggesting all week that sunlight alone helps mature bolls at temperatures greater than ‾50F- even when we aren’t technically accumulating heat units. As evidence, we watched several fields move from 20 to 40 percent open over this past weekend- which many of you will recall was quite cold (temps in the lower 50s). If you take a look at the literature, you will find that there is more to boll maturity than just temperature. The cotton plant may not thrive at 50 or 55 degrees, but producing viable seeds and thereby continuing the species is deeply ingrained in a plants’ genetics. For those that called earlier in the week, I argued that uppermost bolls would continue to mature until temperatures dropped into the mid to low 40s and that I’d plan my defoliation on the latest maturing acres to make sure we capitalized on all sunny days 2020 might offer while keeping a close eye on the forecast- bolls must be open prior to a freeze. The rule of thumb for us is get the first application out no later than the first or second week of October.
I opened this with ‘if you trust the forecast’. I’m not sure I trust much beyond tomorrow and definitely won’t hang my hat on the 14 day forecast. For those that see an opportunity to open up even their latest planted acres next week, I won’t be able to argue against it. The first full week of October doesn’t look promising. But keep in mind that a clear day with a high in the low 70s will still likely allow a boll to mature. . . slowly, but surely. If you decide NOT to hit those latest acres at your next earliest convenience, pay very close attention to the forecast and pull the trigger well before a freeze. I want ethephon on that plant for at least 5-7 days before a freeze. ∆
DR. TYSON RAPER: Cotton & Small Grains Specialist, University of Tennessee
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