Conditioning cotton for increased response to defoliant chemicals

Abstract

Chemical defoliants frequently cause varying amounts of abscission when applied to cotton ( Gossypium hirsutum L.), and almost always become less effective as the temperature is lowered to near 16°C. The objective of this research was to evaluate the effect of TD 1123 (potassium 3,4-dichloroisothiazole-5-carboxylate) in altering leaf abscission response of cotton to the defoliant chemicals DEF (S,S,S,-tributyl phophorotrithioate), dimethipin (2,3-dihydro-5,6-dimethyl-1,4-dithiin 1,1,4,4-tetraoxide), and thidiazuron (N-phenyl-N′-1,2,3-thiadiazol-5-ylurea) in relatively low temperature environments. The tests were conducted in one temperature-controlled greenhouse experiment and two field experiments (early and late season). Measurements of leaf abscission, regrowth, seedcotton yield, and various boll properties were made and the data analyzed statistically. Defoliation response to each of the three defoliant chemicals was significantly enhanced in both the low and high temperature regimes when TD 1123 was applied ten days before the defoliant treatment. The enhancement, however, was more pronounced in the low temperature environment. In addition, regrowth was reduced on the TD 1123-treated plants in both temperature regimes. Seedcotton yield, lint percent, and boll components were not significantly affected by any chemical treatment. The research indicates that TD 1123 can be an effective harvest-aid chemical on cotton when plant and environmental conditions are not conductive to easy defoliation.