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Evaluation of Potassium 3,4-Dichloroisothiazole-5-Carboxylate as a Harvest-Aid Chemical on Cotton¹

Chemical defoliants usually cause varying amounts ofleaf abscission when applied to cotton (Gossypium hirsutum L.). This variation is due mainly to environmental factors, but may also be influenced by plant characteristics. The objective of this research was to evaluate the effect of potassium 3,4-dichloroisothiazole-5-carboxylate (TD-1123) in altering leaf abscission response of cotton to conventional defoliant chemicals. Field and greenhouse studies employed rates of TD-1123 that varied from 0 to 1.12 kg/ha, and timing of application that ranged from 0 to 4 weeks before defoliant chemical treatments. Measurements were made to determine effects of rate and time of application of this chemical on leaf abscission, regrowth development, yield of seed cotton, and various boll and seed properties.

TD-1123 failed to alter leaf abscission response of greenhouse plants when applied as a mixture with DEF (S,S,Stributylphosphorotrithioate), but caused a significant increase in abscission rate and total defoliation when applied 1, 2, or 4 weeks prior to DEF. The 1 and 2-week pretreatments, however, were the most effective in this respect. Regrowth development was also reduced in the 1 and 2-week pretreatments of greenhouse plots, but was increased when applied 4 weeks before DEF. The rates of TD-1123 that gave the greatest abscission response were 0.28 and 0.56 kg/ha. Seed germination, however, was reduced when these rates were applied 4 weeks prior to DEF.

Regrowth, yield, and boll components of field cotton were not affected by TD-1123 at rates of 0.28, 0.56, or 1.12 kg/ha. These rates, however, were equally effective in increasing leaf abscission response to DEF. A 10-day pretreatment of 0.336 kg TD-1123/ha also increased leaf abscission with sodium chlorate and with DEF -f- endothall [7-oxabicyclo(2.2.1)heptane-2,3-dicarboxylic acid] mixtures. This research indicates that TD-1123 can be an effective harvest-aid chemical on cotton.

Key Words: Boll development • Conditioning • DEF • Defoliation • Endothall • Germination • Regrowth • Sodium chlorate • Gossypium hirsutum

² Plant physiologist, ARS, USDA, Stoneville, Miss.

Received for publication August 19, 1977.