Indicators of last effective boll population and harvest aid timing in cotton

Maintaining profitable and sustainable production of cotton (Gossypium hirsutum L.) relies on improvements in management. The objective of this study was to determine the proper defoliation timing to optimize lint yield and fiber quality through calculating heat unit (HU; DD15.5) accumulation beyond cutout, defined as five nodes above white flower (NAWF = 5). Experiments were conducted in Burleson County, Texas, in 2003 and 2004, on a Weswood silt loam soil (fine-silty, mixed, superactive, thermic, Udifluventic Halplustepts). Treatments were applied in a split-plot arrangement using a randomized complete block design with four replications. The main plots consisted of three nodal positions (NAWF = 3, 4, and 5) and the five subplots were HUs (361, 417, 472, 528, and 583) accumulated beyond the corresponding nodal positions (NAWF), at which time a tank-mix of harvest aids was applied. Immediately before defoliation, 10 plants plot(-1) were evaluated for percent open boll (POB) and nodes above cracked boll (NACB). Lint yield was detrimentally impacted in south central Texas when defoliation was initiated at 472 HUs beyond NAWF = 5. Defoliation at 60 POB resulted in as much as 29% more lint yield than defoliation based on the current benchmark of NAWF = 5 plus 472 HUs. This finding suggests NAWF = 5 is neither an indicator of the last effective flower population in all production locations, nor a proper guide for timing cutout on which end-of-season management decisions should be based in south central Texas.