EFFECT OF COTTON DEFOLIANTS ON LEAF ABSCISSION, IMMATURE BOLLS, AND LINT YIELDS IN A SHORT-SEASON PRODUCTION SYSTEM
Chu, CC; Henneberry, TJ; Reynoso, RY
Pink bollworm (Pectinophora gossypiella Saunders), and
associated secondary insect pests have dramatically reduced cotton (Gossypium hirsutum L.)
production in the Imperial Valley of California, resulting in mandated short-season cotton
production practices. Application of a chemical defoliant and/or a growth regulator in August or
September is an important component of the short-season system. Studies were conducted to
determine the effectiveness of various chemical defoliants on cotton lint yield, leaf abscission,
and reduction of late-season fruiting forms under a short-season production system in the
Imperial Valley. Application timing in relation to days after irrigation termination also was
studied. Results showed that Dropp (thidiazuron, N-phenyl-N'-1,2,3-thiadiazol-5-ylurea), Dropp
plus Def (butifos, S,S,S-tributyl phosphorotrithioate), and Ginstar EC [10% thidiazuron and 5%
diuron N'-(3,4-dichlorophenyl)-N,N-dimethylurea], at recommended rates achieved about 80%
defoliation, which was adequate for machine harvest. Dropp, Dropp plus Def, and Ginstar EC were
more effective than Cotton Aide (sodium cacodylate and dimethylarsinic acid), Tumbleaf (sodium
chlorate), Def, and Folex (butifos) in defoliating the plants and in reducing numbers of late
season fruiting forms that serve as host materials for overwintering pink bollworm. Better
defoliation resulted from Drop applications made 2 wk or more after last irrigation than from
applications made 1 wk after last irrigation. Number of open bolls and lint yield were not
affected by the application of defoliant chemicals in the study.