A heat unit method, based on accumulated degree days (DD(60), 90 max) from day of first bloom was used to schedule defoliation timing for 'Stoneville 825,' 'McNair 220,' 'G&P 3774,' and a group of rapid fruiting cotton strains. Five treatments were used to schedule defoliation when 1350, 1475, 1600, 1725 and 1850 heat units had accumulated from day of first bloom of each cotton genotype. Treatments were replicated 7 times in a randomized block, split plot experimental design with cotton genotypes as main plots. All plots were defoliated with 0.22 kg Drop + 290 ml Def/ha applied by ground rig in 103 liters water/ha at 30 psi. First pick and total yields were obtained by harvesting two four-meter row sections from each plot at 7 days after defoliation and 14 days after first harvest.