Thoughts On Terminating Irrigation And Defoliating Our Early Acres

DR. TYSON RAPER

 JACKSON, TENNESSEE

I’ve spent the better part of the past three days walking cotton throughout West Tennessee, and while I’m pleasantly surprised by our earliest planted acres, I’m concerned the crop in many areas may fall well-short of what we might have expected at the end of July. In this blog, I briefly share my thoughts on how I would approach terminating irrigation in 2024 and what I believe may be our best first-shot blend for defoliating our earliest acres.

 Over the past moth, many areas in West TN have not caught more than half an inch of rainfall.  May, June and a decent portion of July were much wetter than I would prefer- far too wet to promote a deep-rooted crop.  As a result, we entered one of the driest Augusts I’ve seen with a very shallow-rooted crop. Retention has generally been high and fortunately, temperatures were mild through much of August. Unfortunately, temperatures are consistently breaking 100 this week and humidity is the lowest I ever recall experiencing from a Tennessee August.  Keep in mind that atmospheric demand in a hot, dry environment is much higher than in a hot, humid environment.  As a result, this crop quickly transpired through most soil water reserves.

 While the crop tolerated the first couple weeks of August quite well, widespread observations of cavitation began early last week.  Our earliest planted acres had fortunately matured much of the crop before the severe drought stress developed, but boll sizes do appear to be smaller and many bolls in the top of the plant will likely not be filled.  I’ve visited with many over the past two weeks concerning irrigation termination.  Typically, we would suggest terminating irrigation at first cracked boll.  Many of those studies were conducted in an environment very different from the one we are currently experiencing- and in a different crop than the one we are walking.  In my opinion, I would strongly encourage you to continue irrigating past cracked boll during 2024, with a target termination of closer to 10-15% open.  Our dry environment should assist in drying out those open bolls to prevent promotion of boll rot or fiber degradation.  Unless we get a substantial amount (2+ inches) this weekend, expect our latest planted acres to continue to need irrigation water for the foreseeable future.

 Defoliating our earliest acres will be complicated if we catch rain in the next two weeks.  For those that are considering defoliating next week, I would encourage you to lean heavily on thidiazuron. Thidiazuron is the go-to product for regrowth control and the product performs very well in warm conditions (night temps above 65F).  I’m also running tribufos in this load to help get across what is a very thick, tough cuticle.  If you decide to treat in the following week, I’d look at 3.2 oz/ac Dropp/Daze with 2 oz/ac Folex with 16-24 oz/ac ethephon.  Blending Finish in to replace some of the ethephon load will also likely help on regrowth control. Ginstar is not a product I would use until night temps fall below 60F.  ∆

DR. TYSON RAPER: University of Tennessee