Defoliation Window Closing?

DR. TYSON RAPER

JACKSON, TENN.
   If historical weather trends are true and our forecast holds, we are staring at one of the last opportunities to use moderate to warm temperatures to coax leaves off and open bolls. The long term forecast suggests low temperatures next week will consistently fall below 60F with a few nights forecast to touch the low 50s. Furthermore, rain is in the forecast over the weekend/through the beginning of next week.
   Over the past few days, I’ve visited with several who have considered waiting to apply the first harvest aid application to late cotton until the crop gets closer to mature. There are several things I’d like to mention for those in that scenario.
   First, when temperatures drop into the low 50s to upper 40s, we do not accumulate heat units. While the plants are still technically alive, all physiological processes associated with boll maturity screech to a very slow pace. If we do not warm back up after next week, don’t expect the maturity of bolls to change much from their current status.
   Second, it is much easier to shed leaves and crack bolls in warm temperatures with clear skies. While the chances for rain the middle of next week are not great, most days either cloudy or partly cloudy. As we move into mid and late October, chances of cloudy conditions and/or rain increase.
   Finally, we are currently running warmer than the 30 year average. . . it is time to start considering the calendar. I am a firm believer in having the first shot of harvest aid out prior to the 10th of October.  Likelihood of bolls maturing much past this date are slim. Likelihood of a frost increases substantially every day past the 15th.  Having favorable conditions for defoliation and harvest quickly degrade after this date.
   Products and Rates
   Coupled with cooler night temperatures, we will need to increase rates to achieve the same responses noted under warm and clear conditions. I will not be using straight thidiazuron products after this week. Furthermore, I’m hesitant to include thidiazuron+diuron mixtures after Monday; if you chose to use those products (Ginstar, Adios, etc) you will be forced to use very stout rates. Should conditions change quickly and a few cloudy days turn to clear days, expect to stick leaves. My first-shot mixture next week will consist of a stout shot of tribufos (Folex) plus a healthy dose of boll opener. ∆
   DR. TYSON RAPER: Cotton & Small Grains Specialist, University of Tennessee