Evaluation of defoliant mixtures in cotton

Abstract

Current chemical defoliants have limitations which are usually magnified by environmental conditions or the nature of the compound. The objective of this study was to evaluate the effectiveness of various chemical defoliants when used in combination at one-half the standard use rate. Tests were conducted from 1986 to 1988 at the Delta Branch Experiment Station in Stoneville, Mississippi and in 1987 and 1988 at the Plant Science Research Center in Starkville, Mississippi. Chemicals evaluated were tribufos (S,S,S-tributylphosphorotriphioate), thidiazuron (N-phenyl-N prime-1,2,3-thi-diazo-5-ylurea), dimethipin (2,3-dihydro-5,6-dimethyl-1,4-dithiin 1,1,4,4 tetraoxide), and ethephon [(2-chloroethyl)phosphonic acid]. Standard rates for each chemical defoliant were 1.26, 0.14, 0.35, and 2.24 kg/ha, respectively. When used in two-way combination treatments, each defoliant rate was reduced by one-half. A non-ionic surfactant at 0.25% ( v/v) was added to all dimethipin treatments. Defoliation and regrowth estimates were made by visual observations at 5, 7, and 14 days after treatment. In general, two chemical defoliants tank-mixed at one-half the standard use rate were equal to or superior to either single component applied at the standard use rate. In addition to equal effectiveness, combinations offered additional safeguards against adverse environmental conditions.