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Termination of Late Season Cotton Fruiting with Plant Growth Regulators¹

Chemical termination of cotton (Gossypium spp.) fruiting is a new proposed insect control technique. Development of effective fruiting termination treatments is the objective of this research. Treatments were applied to field plots (11 to 20 m long) between 15 August and 10 September. We found two types of plant-growth-regulator response: 1) fast acting and non-persistent; and 2) slow acting and persistent. Mixutres of the two types produced the most effective chemical termination treatments. Two effective growth regulators of each type were identified. The slow acting, persistent growth regulators were chlormequat or CCC, [(2-chloroethyl)trimethylammonium chloride], and chlorflurenol, (methyl 2-chloro-9-hydroxyfluorene-9-carboxylate). The fast acting growth regulators were 2,4-D. [(2,4-dichlorophenoxy) acetic acid], and TD 1123, (3,4.dichloroisothiazole 5-carboxylic acid). 2,4-D was applied at 37 g/ha when used alone, and usually at 28 g/ha in mixture with other plant growth regulators. The most effective rates for chlormequat and chloroflurenol were 560 g/ha in mixture and about twice that rate when applied alone. TD 1123 was applied in mixture at 1121 g/ha. Mixtures of 2,4-D with either of the two persistent growth regulators produced more effective chemical termination than 2,4-D applied alone. These three treatments have been tested extensively and found effective. They are suitable for use by entomologists for large scale testing of chemical termination for insect control. In limited testing, TD 1123 appeared to be superior to 2,4-D when used in mixture with the persistent plant growth regulators.

Key Words: Gossypium hirsutum L. • Gossypium barbadense L. • 2,4-D (2,4-dichlorophenoxy) acetic acid • 3,4-dicholoroisothiazole 5-carboxylic acid • CCC • Chlormequat • (2-chloroethyl)trimethylammonium chloride • Chlorflurenol • Methyl termination • Seed quality • Fiber quality • Seedling emergence

² Agronomists, ARS, USDA and Univ. of Arizona, respectively, Univ. of Arizona Cotton Res. Center, 4207 Esat Broadway, Phoenix, AZ 85040.

Received for publication August 10, 1976.