With the exception of a few rainy days, we have had a very nice window for defoliation. Unfortunately, the forecast for the beginning of this week (9/26-10/1) includes night temperatures in the low 50s and high 40s with daytime temperatures below 80F. As night temperatures drop from 65F to 50F, remember that plant responses to defoliants and boll openers slow to a crawl; applications which seemingly blew bolls open within a day or two will now take much longer to work and some products will have almost no impact on boll opening or defoliation. Rates of defoliants and boll openers will have to be increased to compensate for the reduction in product efficacy noted at lower temperatures. For those contemplating a first or second shot this week there are several key points to keep in mind.
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- For all applications:
- If possible, delay applications until night temperatures rise back into the 50s.
- Stand alone thidiazuron products (Dropp, Freefall, Klean-Pik, etc.) should not be in the mix until we move back into warmer temperatures (night temps above 65F).
- Even with cool temperatures, the forecasted clear conditions should increase application efficacy. Fortunately, the next four out of seven days are predicted to be sunny or partly sunny.
- Still, expect very slow leaf shed and boll opening.
- First shot applications:
- Predictably coaxing leaves off with minimal chances of sticking leaves at night temperatures below 65F will rely on a stout rate of tribufos (Folex) OR thidiazuron+diuron (Adios, Ginstar, etc.). As temperatures drop from 60F to 55F, these products become much less effective and PPOs have to be considered.
- Selecting rates of PPOs and adjuvants for a ‘first shot’ is tricky, especially where large mainstem leaves and juvenile growth remain on the plant. I prefer to place the PPOs in a scenario where most mature leaves have been removed and only juvenile growth or a few scattered mature leaves remain.
- Boll opening products (even those containing cyclanilide like Finish or Terminate) work best at temperatures above 60F. Higher rates will be necessary if boll opening is required at lower temperatures.
- Second shot applications:
- The best option for removing juvenile growth and a few scattered mature leaves in a second shot at temperatures below 60F will likely be a PPO. In this scenario, the PPO will either injure the green material enough to cause it to shed or it will stick it to the plant; either way, the PPO will eliminate green material in picked seedcotton.
- If only mature leaves remain, a stout rate of tribufos (Folex) might be a good option.
- Again, boll opening products (even those containing cyclanilide like Finish or Terminate) work best at temperatures above 60F. Higher rates will be necessary if boll opening is required at lower temperatures.
Rates, products and combinations which have been alluded to within this post are defined in greater detail within the 2016 MidSouth Defoliation Guide. For additional information, or to learn more about factors influencing product efficacy and defoliation timing, click the table or link above.
