ABSTRACT

Field experiments were conducted from 1987 through 1991 at the Delta Branch Experiment Station, Stoneville, MS to determine the effects of postemergence topical application of 1.0 lb ai/A fluometuron plus 0.25% (v/v) nonionic surfactant 2.0 lb ai/A MSMA, and a combination of 1.0 lb ai/A fluometuron plus 2.0 lb ai/A MSMA on cotton yield, fruiting profile, and fiber characteristics. The cultivar IDES 4221 was planted in 1987 and 'DES 119' was planted in 1988 through 1991. In addition, a second cultivar 'DPL 50' was planted in a duplicate study in 1990. Herbicide treatments were applied with a CO₂-pressurized backpack sprayer in a volume of 20 gallons per acre to cotton in the cotyledon to one true leaf development stage. Treatments were arranged in a randomized complete block design with four replicates. Cotton was hand harvested beginning when approximately 20% of the bolls were open in the untreated control and repeated at 7 to 10 day intervals for five harvest periods.

Between 1988 and 1991, fluometuron or MSMA caused 4 to 28% visual injury to cotton up to 28 days after treatment. Both, however, were less injurious than the combination of fluometuron plus MSMA, which caused between 10 and 34% injury.

Seed cotton yields at the first harvest interval were significantly reduced by all herbicide treatments except in 1987 and with DES 119 in 1990. At the second harvest interval in 1990, the yield of DES 119 treated with MSMA and fluometuron plus MSMA was significantly less than the untreated control. Cotton yields in herbicide-treated plots at later harvest periods were equal to or greater than the control. All herbicide treatments significantly reduced total seed cotton yield in 1988. Fiber length, strength, uniformity, and micronaire were not adversely affected by topical herbicide treatments.

Compared to the control, the number of sympodia per plant and effective sympodia was not affected by the herbicide treatments. The number of monopodia per plant was reduced by all herbicide treatments in 1990. This variable was not affected in other experiment-years. Compared to the untreated, fluometuron reduced the percent of bolls on sympodia attached to monopodial branches (percent monopodial bolls) in 1989, while MSMA reduced the percent manopodial bolls on DES 119 in 1990. Fluometuron plus MSMA, compared to the untreated control, reduced the % monopodial bolls on both cultivars in 1990 and in 1991.

Four experiment-year averages revealed no significant differences among herbicide treatments compared to the control in the total number of bolls per plant, percentages of bolls in first, second, or outer positions, highest sympodium with two bolls, or number of sympodia with bolls in the first or second positions. However, MSMA and fluometuron plus MSMA increased the node number of the first sympodia by one and one and one-half positions, respectively, compared to the control.