COTMAN defoliation rules were evaluated in three large plot on-farm trials. COTMAN defines cutout as the date when the average number of nodes above the uppermost first position white flower equals 5 (NAWF = 5). COTMAN further recommends defoliation once 850 heat units (HU's) have been accumulated beyond cutout. Two fields were evaluated in Mississippi County (northeast Arkansas) and one field in Jefferson County (southeast Arkansas). Within each location, defoliation treatments were applied based on COTMAN recommendations and based on conventional producer practices for timing defoliation. Plots were machine harvested and seedcotton yields of the defoliation treatments compared. Seedcotton yields were not significantly different in 2 of 3 trials. Seedcotton yields from plots defoliated based on COTMAN rules were significantly lower at one location in Mississippi county. Harvest at this location however, was seven days earlier for plots defoliated based on COTMAN recommendations. Data from all locations support the use of COTMAN as a tool for timing defoliation. COTMAN may also help facilitate earlier harvest and reduce end-of-season risk.