The current forecast has 2-3 days of likely rain starting Saturday, so it might be wise to pump the brakes on defoliation after today (Thursday). When we defoliate, we want a couple of days of sunny weather to activate defoliants but more importantly, we want to avoid cracking bolls just ahead of rains that last more than a day or so. This is more important in fields with a higher number of unopened bolls versus only a few, very mature unopened bolls remaining. Resuming defoliation once this rain passes and when more sunny weather is expected will likely improve the outcome

Next week will bring cooler temperatures as well. As we expected, regrowth has been something to contend with thus far. This will continue, but we also expect it to slow down a little bit with the expected cooler weather. If you are currently using a TDZ-based tankmixture for regrowth, we expect the activity of TDZ to slow down and efficacy to decrease, as there are several nights expected to be in the 40s or very low 50s. Daytime temperatures are expected to be in the 70s in most areas so we’ll still see some activity from TDZ, but it won’t likely be as effective as it has been thus far. This coming week would be a good time to transition to a TDZ+diuron mixture. For fields with very few bolls remaining to open and the unopened bolls are very mature, 8 oz of TDZ+diuron with 32-42 oz ethephon would be an effective tankmixture. For fields with several closed bolls that are borderline or questionable in maturity, 1 quart of Finish/Terminate, perhaps spiked with ethephon up to 10.5 oz, and 6.4 oz TDZ+ diuron would be effective. The TDZ+diuron rate in this mixture can be increased to 8 oz/A if daily highs consistently fall into the 60’s with nights consistently in the 40’s. For those who want to continue using TDZ in their tankmix through next week, because it has already been purchased, make sure to use no less than the 3.2 oz rate, but don’t expect the same results that you have observed to date. Drastically increasing the TDZ rate is also not advised, especially when mixed with Finish or Folex, which can drastically increase the risk of desiccating leaves.

Keep in mind that no tankmixture will hold back regrowth effectively beyond 2 weeks after application, hence why we recommend only defoliating as much as can be harvested 2 weeks later. Switching from a TDZ-based tankmixture to a TDZ+diuron-based mixture is the best way to hold back and control regrowth, but even it will break beyond 14 days after application, just to a lesser degree.

Next week will be cooler but we will still accumulate a few heat units for a little while. This will likely gradually slow down throughout the month of October. As a reminder, our very recent research suggests that defoliating the latest maturing fields by mid October greatly improves the odds of opening later set bolls, versus waiting until early November when we typically expect to encounter our first frost. In other words, there is little incentive and greater risk associated with delaying defoliation of the latest maturing fields beyond mid October.