COTMAN, a computer-aided cotton management program, was used to monitor approximately 80 acres of cotton in Mississippi county located in northeast Arkansas during the 1999 cropping season. Nodes-above-white-flower (NAWF) data, generated from COTMAN, was used to define the date of the last effective boll population (ie. Cutout or NAWF = 5). Heat unit (HU) accumulations were calculated beginning at the date of cutout by subtracting 60⁰F from the average daily temperature. Replicated defoliation treatments were initiated in northeast Arkansas at approximately 650, 750, 850, and 950 HU's past cutout. Yield and fiber quality were compared in an effort to validate initial research efforts. No significant differences were observed in fiber micronaire, strength or length for plots defoliated at any of the four HU treatments. A greater percentage of seedcotton yield was obtained in the first harvest for plots defoliated at 948 HU's past cutout than for plots defoliated at 661 HU's past cutout. However, no yield penalty was recorded when defoliation was initiated at 763 (or more) HU's past cutout. Results of this study help to confirm that HU accumulations past cutout are an effective means of defining crop maturity. These results further indicate defoliation can be successfully timed based on HU accumulations beyond cutout.