Timing of application for defoliants affects lint yield and fiber quality of cotton (Gossypium hirsutum L.). Nodes above cracked boll (NACB) is one technique to determine defoliation timing. A defoliation timing study based on the NACB method was evaluated to determine the effects of premature and delayed defoliation on lint yield and fiber quality. Field experiments were conducted from 2003 to 2004 at the Delta Research and Extension Center, Stoneville, MS, on a Bosket very fine sandy loam (fine-loamy, mixed, active, thermic Typic Hapludalfs) soil. Treatments consisted of a standard defoliant/harvest-aid combination applied at 10, 8, 6, 4, and 2 NACB and three cultivars (ST 4892BR, SG 215BR, and PM 1218BR). Lint yield for PM 1218BR was higher than SG 215BR both years of the study. Percent lint was consistently higher for ST 4892BR. Lint yields varied over years with respect to defoliation timing based on NACB. In 2003, defoliation at 6 NACB resulted in an addition of approximately 72 lb/A lint compared to the 8 NACB timing. In contrast, lint yields were reduced when defoliation occurred at 6, 8, and 10 NACB compared to the 4 NACB timing in 2004. Delaying defoliation from 6 to 4 NACB resulted in an addition of approximately 141 lbs/A lint. Delaying defoliation until 2 NACB did not reduce lint yield either year. These results suggest boll distribution on the plant should be considered before applying defoliants based upon NACB timing recommendations. Percent lint was lower when defoliation occurred at 10 NACB compared top the 6, 4, and 2 NACB timings. Defoliation at 2, 4, and 6 NACB resulted in higher micronaire readings than the 8 and 10 NACB timings both years. Overall, fiber qualities were less sensitive than lint yield to defoliation timing by the NACB method in this study.
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