There comes a point late in the season where defoliation timing begins to lean more heavily on the forecast and historical temperature normals associated with the current date than our maturity measurements (NACBs, %open, uppermost harvestable boll maturity as determined by the sharp-knife technique, etc.).  In West Tennessee, I would argue that we are very rapidly approaching that time frame.  The 5 day forecast here on the 28th day of Sept. for West TN indicates the next few days appear to be very favorable for defoliation applications, but conditions degrade by the end of the week.  The long-term forecast does indicate the end-of-week dip may be followed by moderate temperatures- still, instead of trusting a fairly unreliable 10 day forecast, I’d weigh those forecasted temperatures with the temperature normals for your area.

Remember that if we do wait on that last boll to mature we are increasing the time those lower position bolls are open and exposed to Mother Nature. Gambling on higher yields by delaying defoliation may payout, but the wager is both the quality and the ability to pick those bolls that contribute the most to the bottom line.  Risking those ‘money’ bolls for the ‘top crop’- which generally contributes the least amount to our bottom line- is a risk that I do not like to take.   Furthermore, keep in mind that our boll opening materials are very dependent upon temperature, and as our minimum temperatures move below 60F we begin to see a substantial decline in effectiveness.

To summarize, I’d like to quote Dr. Keith Edmisten at NC State: “The later one waits to defoliate the less likely they will have decent weather to defoliate. When the growers call and its 50 degrees and they want to know if they should use nuclear waste to defoliate cotton there will be no good answers.”