A three year study was conducted to evaluate the effects of defoliants applied early (40-50% bolls open) and late (65-75% bolls open) on cotton yield and quality. the defoliants evaluated were Def (1½ pt/A), Ethrel (3 qts/A),Def (1 pt/A) plus Ethrel (1 qt/A) and Dropp (0.2 lb/A). Plots were four rows (40" wide) and 370 feet long with a high cycle type sprayer with three nozzles per row in 20 gallons of diluvent per acre. Experiments were located in the same field all three years at the Tennessee Valley Substation in North Alabama.

Boll counts sevens days after application indicated that early application of Ethrel increased the number of open bolls to greater than 90% for 1980 and 1982. Later Ethrel applications did no improve boll opening as much as early applications. Year differences were more evident in the defoliation results than in the maturity indicators. In 1981, all treatments performed effectively for cotton defoliation except for early applications of Ethrel. In 1982, Ethrel and Dropp applied early provided acceptable defoliation. Later applications of the defoliants did not provide effective leaf drop. Cool weather conditions were present at the time of the late season applications.

The percent of cotton harvested at first picking was 90% or greater for those plots receiving Ethrel for all three years and all application dates. Cotton receiving applications of Def had numerically the lowest percent harvested at first picking of all treatments including the untreated check. Cotton yields were similar with years for both early applications and late application for all three years.

The selection of defoliants had no influence on fiber quality by application timing affected several properties. In 1980, late applications reduced length, uniformity, strength and fiber elongation. In 1981, late applications also reduced micronaire values. Early applications reduced percent non-lint after ginning in 1981.