Since 1998, researchers from across the Cotton Belt have come to different conclusions on the optimum defoliation time based on heat unit accumulation from cutout (NAWF=5). COTMAN, a cotton-management expert system based on in-season plant monitoring recommends that defoliation be initiated at 850 accumulated heat units from cutout. Utilizing an upper limit temperature threshold could possibly explain differences in results of defoliation timing and recommendations from across the Cotton Belt. An upper limit temperature threshold would impact the number of daily heat units that are accumulated in the southern areas of the Cotton Belt.

For the past three years, defoliation timing studies have been implemented in several locations across the Cotton Belt to compare the effects of utilizing an upper limit temperature threshold in calculating daily heat units. Treatments consisted of three different upper limit temperature thresholds (90°F,95°F, and no upper limit) and defoliation at five maturity stages based on 650, 750, 850, 950, and 1050 accumulated heat units from date of cutout.