Date of Award

1999

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Plant, Environmental Management and Soil Sciences

First Advisor

Eric P. Webster

Abstract

Multi-source regression models describing the control of alligatorweed with bensulfuron-methyl as influenced by rate and temperature were developed under field conditions. Temperature models describing the activity of bensulfuron-methyl at 21 to 84 g ai/ha on alligatorweed were linear 7 days after treatment (DAT) and quadratic 14 and 28 DAT. At 7 and 14 DAT, a minimum average temperature of 14 C was required for bensulfuron-methyl activity on alligatorweed. The temperatures for optimal alligatorweed control with bensulfuron-methyl at 14 DAT ranged from 21 to 24 C with rates of 21 to 84 g/ha. Temperatures for optimal alligatorweed control with bensulfuron-methyl at 28 DAT ranged from 21 to 22 C with rates of 21 to 84 g/ha. Overall, the results indicate that alligatorweed control with early season bensulfuron-methyl applications may not be optimal when temperatures are less than 20 C or above 23 C. Laboratory studies were conducted to evaluate influence of soil type and pH on the adsorption of bensulfuron-methyl. Four Louisiana rice soils, Caddo-Messer silt loam, Crowley silt loam, Gigger silt loam, and Sharkey clay were used. Soil type influenced to a relative degree of soil binding of bensulfuron-methyl. Freundlich constants for Caddo-Messer silt loam, Crowley silt loam, Gigger silt loam, and Sharkey clay soil were 2.56, 0.95, 13.9 and 2.99 respectively. The pH of the four soils did not correlate with the relative degree of soil binding with a R2 = 0.01. Organic matter and clay content were correlated with soil binding with a R2 = 0.21 and 0.35, respectively. Cation exchange capacity had the greatest influence on soil binding with a R2 = 0.49. The Crowley silt loam soil was used to evaluate the influence of pH on bensulfuron-methyl adsorption. Freundlich constants at pH 5, 6, 7, and 8, were 6.38, 3.96, 3.48, and 4.73, respectively. As pH increased K showed a downward trend, toward decreased adsorption. The poor fit of data at pH 7 and 8 prevented a stronger assessment of the data. Studies were conducted to evaluate herbicides in combination with bensulfuron-methyl to evaluate possible tank-mix partners. Treatments that contained triclopyr had increased control of alligatorweed and was more consistent than the other treatments.

ISBN

9780599372764

Pages

88

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