R. J. Thullen and P. E. Keeley

OBJECTIVES: To identify effective systems for the control of annual morningglory in cotton.

PROCEDURES: Several treatments were applied to field plots at the USDA Cotton Research Station in 1989 and 1990 for the control of annual morningglory in cotton. Herbicides were first applied to planting beds at cotton planting in early April and incorporated with a mulcher operated 5 em or 10 em deep in the soil. Rates for these early treatments were 2. 0, 2. 0, and 1. 6 lbs/A, respectively, for cyanazine, methazole, and prometryn. Post emergence and layby treatments were applied as directed sprays to weeds in the drill row at the base of the cotton plants. Post-emergence treatments began soon after the middle of May, whereas the layby treatments were not applied until the end of June. Rates were 1.0 lb/A for cyanazine, 0.5 to 1.5 lbs/A for methazole, and 0.7 to 1.6 lbs/A for prometryn. Although all plots were conventionally cultivated, some were cultivated with special equipment (rods/torsion weeders/spring weeders) to remove small morningglory in the drill row of cotton. When rods were used, plots were cultivated in opposite directions. This cultivation and handweeding were both performed near the end of May. See Table 1 for more information about treatments.

RESULTS: The most successful herbicidal treatment for the control of annual morningglory in cotton was postemergence applications of 1.0 lb/A cyanazine + 2.0 lbs/A MSMA in early June (Table 1). Applications of cyanazine + MSMA to cotton at layby in late June was also helpful in reducing yield losses of cotton. The only other herbicide that provided significant postemergence activity was prometryn. Prometryn incorporated 10 em deep provided the most consistent control of the soil-incorporated herbicides. But control with this treatment was incomplete based on both visual control ratings and harvested cotton (Table 1). Although the cultivator equipped with rods removed many small morningglory plants in the drill row of cotton, too many survived. Based on the results of the handweeding treatment in late May of 1989 and 1990, the weed-free period for morningglory will probably have to extend at least until the middle of June.

FUTURE PLANS: A manuscript of this two year study is being prepared. A second study will begin on the area of this morningglory nursery in the spring of 1991.

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