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Timing Late-season Fruiting Termination of Cotton with Potassium 3,4-Dichloroisothiazole-5-Carboxylate¹

A plant growth regulator, Pennwalt TD-1123³ (3,4- dichlorolsothiazole-5-carboxylic acid) was evaluated as a chemical termination agent for reducing fruit set on cotton (Gossyplum spp.) in 32 tests in Arizona and California from 1974 through 1977. A reduction in immature bolls through chemical termination causes a similar reduction in diapausing pink bollworms [Pectinophora gossypiella (Saunders)]. In most tests, TD-1123 was applied in mixture with a persistent plant growth regulator, which was used to prevent plants from recovering from TD-II23 effects and renewing fruiting. The timing of TD-1123 application was found critical for obtaining maximum reduction of immature bolls at harvest and minimum reduction of yield and quality. The formula "harvest date, less average number of days from flowering to boll maturity for that date, plus seven’ gave a nearoptimum time for treatment. The ratio of the actual number of days from treatment to harvest to the suggested number of days was used to evaluate treatments used in previous tests. Early application (ratio greater than 1) of TD-1123 moderately reduced the yield of southeastern Upland (Delta type) cotton (G. hirsutum L.) cuitivars, but greatly reduced yields of Acala (G. hirsutum L.) and American Pima (G. barbadense L.) cottons. With the suggested application date (ratio 1.0), immature bolls were reduced about 95% on southeastern Upland cotton, 75 to 80% on Acala cotton, and 60% on Pima cotton.

Key Words: Gossypium hirsutum L. • Gossypium barbadense L. • Pink bollworm • Pectinophora gossypiella (Saunders) • Plant growth regulator • Chemical termination.

² Agronomist, USDA, SEA-AR, Univ. of Arizona Cotton Res. Center, 4901 East Broadway, Phoenix, AZ 85040; agronomist, Univ. of Arizona (deceased); entomologists, USDA, SEA-AR, X~Testern Cotton Res. Lab., 4135 East Broadway, Phoenix, AZ 85040; and plant physiologist, USDA, SEA-AR, U.S. Cotton Res. Stn., 17053 Shafter Ave., Shafter, CA 93963.

Accepted for publication October 22, 1979.