Document Type

Thesis - Open Access

Award Date

1987

Degree Name

Master of Science (MS)

Department

Entomology

First Advisor

David D. Walgenbach

Abstract

The ability of a pesticide to provide the desired level of control may be lost or diminished after repeated soil applications with the same chemical. The microbial population of the soil may develop the capacity to rapidly degrade a-compound to which it has been repeatedly exposed. This loss of persistence due to rapid degradation of a compound by an adapted microbial population is known as enhanced microbial degradation, or enhanced biodegradation. In 1949 Audus showed that failure of 2,4-D to control weeds in soil receiving prior applications was due to a microbiological factor which rapidly degraded the compound. The loss of weed control in New Zealand plots which had received at least three successive applications of EPTC was reported by Rahman et al. Further studies showed that enhanced microbial degradation was responsible. Bufencarb, a carbamate corn rootworm insecticide did not give satisfactory control in South Dakota field trials in 1971 and 1972. Poor performance was also reported in Illinois and Nebraska field trials. By 1974 the Extension Service in Iowa no longer suggested it be used for rootworm control. The organophosphate insecticide isofenphos failed to control rootworms in University of Wisconsin field trials in 1982. It was removed from the market the following year due to widespread complaints about its performance for rootworm control. Coats et al. subsequently showed enhanced biodegradation in the field and laboratory. Felsot et al. reported poor control of corn rootworm in several fields in Illinois where carbofuran, a systemic carbamate soil insecticide, had been applied annually for three or more years. Lack of persistence was determined to be the problem. Sterilization of soils via heat, gamma irradiation, or antibiotics destroyed the soils ability to rapidly degrade carbofuran. This suggested the presence of a biological mechanism responsible for the rapid disappearance of the compound. Other studies have also shown that carbofuran may be rapidly lost in soils receiving prior applications. Ahmad et al. and Gorder et al. did not see a connection between prior use of carbofuran and decreased persistence in laboratory treatment of several soils. In 1984 reports of poor rootworm control came from several locations in eastern South Dakota. An investigation was initiated to follow insecticide persistence patterns in these soils both in the field and in the laboratory. Objectives of the study were to determine if insecticide persistence patterns at these locations indicated that a rapid loss of the insecticide was responsible for lack of control, and to determine if rapid degradation could be induced in the laboratory through successive soil treatments with the same chemical.

Library of Congress Subject Headings

Pesticides -- Biodegradation

Soil degradation

Corn -- Diseases and pests -- Control

South Dakota State University Theses

Format

application/pdf

Number of Pages

96

Publisher

South Dakota State University

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