Masters Theses

Date of Award

5-1989

Degree Type

Thesis

Degree Name

Master of Science

Major

Plant, Soil and Environmental Sciences

Major Professor

G. Neil Rhodes Jr.

Committee Members

Elmer L. Ashburn, Robert M. Hayes, William A. Krueger

Abstract

Field studies were conducted in 1987 and 1988 to determine the utility of imazethapyr in soybean [Glycine max (L.) Merr.] weed management systems. The objectives of these studies were to 1) determine the utility of imazethapyr in combination with other preemergence herbicides, 2) determine the optimum rate of preemergence imazethapyr when followed by various postemergence treatments, 3) determine the optimum rate and timing of postemergence imazethapyr and 4) determine the effect of soil pH on activity of imazethapyr.

Research was conducted at Crossville and Spring Hill to determine the utility of imazethapyr when used in combination with other preemergence herbicides. At both locations in 1987 and at Crossville in 1988, herbicide treatments included preemergence imazethapyr at 0.07 or 0.09 kg ai/ha alone or in combination with pendimethalin at 0.84 kg ai/ha, imazaquin at 0.07 kg ai/ha, imazaquin + pendimethalin at 0.07 + 0.84 kg ai/ha, metribuzin at 0.28 kg ai/ha, chlorimuron + metribuzin at 0.04 + 0.24 kg ai/ha or alachlor at 2.24 kg ai/ha. At both locations in 1987 and at Crossville in 1988, preemergence imazethapyr alone or in combination with other preemergence herbicides provided good to excellent (80 to 98%) control of tall morningglory [Ipomoea purpurea (L.) Roth], entireleaf morningglory (Ipomoea hederacea var. integriuscula Gray), ivyleaf morningglory [Ipomoea hederacea (L.) Jacq.], pitted morningglory (Ipomoea lacunosa L.)( common cocklebur (Xanthium strumarium L.) and jimsonweed (Datura stramonium L.) throughout the growing season.

Research was conducted at Crossville and Knoxville in 1987 and 1988 to determine the optimum rate of preemergence imazethapyr when followed by various postemergence treatments. Herbicide treatments included preemergence imazethapyr at 0.07, 0.09 or 0.11 kg ai/ha followed by no treatment, cultivation or postemergence sethoxydim at 0.21 kg ai/ha, acifluorfen at 0.43 kg ai/ha or imazethapyr at 0.09 kg ai/ha. Postemergence treatments were also applied to plots with no prior preemergence herbicides. Postemergence treatments were applied when morningglories were 12 to 20 cm in height. Preemergence imazethapyr alone provided good to excellent (80 to 99%) control of tall morningglory, ivyleaf morningglory, pitted morningglory, common cocklebur and jimsonweed. There was no added benefit from sequential postemergence treatments.

Separate studies were conducted at Crossville and Knoxville in 1987 and 1988 to determine the optimum rate and timing of postemergence imazethapyr. Herbicide treatments included imazethapyr at 0.07, 0.09 and 0.11 kg ai/ha applied when morningglories were 2 to 10, 12 to 18 and 20 to 30 cm in height. Imazethapyr applied to weeds 2 to 18 cm in height provided good to excellent control (80 to 98%) of pitted morningglory and ivyleaf morningglory, and fair to good (60 to 89%) control of common cocklebur. Imazethapyr at all rates and timings of provided excellent (≥90%) control of jimsonweed. Poor to fair (50 to 70%) control of common cocklebur and morningglories resulted when imazethapyr was applied to 20 to 30 cm weeds.

Greenhouse studies were conducted to determine the effect of soil pH on activity of imazethapyr. Soybean, morningglory and cocklebur were planted in soils with a pH of 5 or 7 and treated with imazethapyr or imazaquin at rates of 0.07 and 0.036 kg ai/ha. Plant fresh weights and dry weights were not reduced by herbicide treatments at either pH. In all cases however, fresh weights and dry weights tended to be greater at the lower pH regime.

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