Doctoral Dissertations
Date of Award
8-1991
Degree Type
Dissertation
Degree Name
Doctor of Philosophy
Major
Plant, Soil and Environmental Sciences
Major Professor
Robert M. Hayes
Committee Members
G. Neil Rhodes Jr, William A. Krueger, John E. Foss, Otto J. Schwarz
Abstract
Pendimethalin (N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine) and flumetralin(N-ethyl-N-(2-chloro-6-fluorobenzyl-2,6-dinitro-α,αα-trifluorop-p-toluidine} are dinitroanilines used for weed and sucker control, respectively, in tobacco. Use of both compounds can cause enhanced injury to crops following tobacco through an interaction. Experiments were conducted to determine if this interaction results from the increased persistence of one or both pesticides. The influence of soil and environmental factors on the persistence of these pesticides and the best model to describe their degradation in soil were evaluated.
Pendimethalin and flumetralin, alone or in combination, were applied to four soils and incubated under four environments for five time intervals. A completely randomized design with a factorial arrangement of treatments was used. Soil concentrations of the pesticides were determined by chemical assay using high performance liquid chromatography. Half-life for each pesticide, alone and in combination, was calculated using the first-order degradation model. The influence of soil properties on pesticide persistence was analyzed by linear correlation with half-lives. Temperature effects on the pesticide degradation rates were determined using activation energies. Effects of soil, soil water content, and temperature on residual phytotoxicity to corn were analyzed. Soil concentration data were fit to several degradation models and compared for the best fit of the data.
Pendimethalin half-life was shortest in a Decatur clay loam. Flumetralin half-life was shortest in a Dickson silt loam. Flumetralin half-life was longer than the pendimethalin half-life in all soils except the Dickson silt loam. Pendimethalin and flumetralin half-lives, when applied in combination, were not significantly different from half-lives of that pesticide alone, so the interaction is not due to increased persistence. Pesticide half-lives were longer at 15 C than 30 C. No difference in half-lives either pesticide occurred between soil water contents. Soil properties were not highly correlated with persistence. Activation energy was lowest for flumetralin and in the Dickson silt loam soil, indicating possible differences in degradation pathways between pesticides and between soils.
Initially, pendimethalin and flumetralin were equally phytotoxic to corn, with differences over time resulting from temperature and soil effects on pesticide persistence. Observed response of the combination treatment, as the percent of the untreated control, was greater than the calculated expected response although the interaction was not significant. Pesticides were phytotoxic longer in a Sequatchie loam than in the Dickson silt loam.
The biexponential and quadratic models had higher coefficients of determination (r2) than the first-order model. Little difference was seen between the first-, second, or zero-order models. Higher r2 values were observed under conditions favoring more rapid degradation.
Recommended Citation
Herrmann, Jeffrey Eric, "Influence of soil and environmental factors on the persistence and phytotoxicity of pendimethalin and flumetralin. " PhD diss., University of Tennessee, 1991.
https://trace.tennessee.edu/utk_graddiss/7558