John M. Wirtz

Document Type

Thesis - Open Access

Award Date

1971

Degree Name

Master of Science (MS)

Department / School

Entomology

First Advisor

P.A. Jones

Abstract

The western corn rootworm Diabrotica virgifera Le Conte, and the northern corn rootworm Diabrotica longicornis Say, are major pests affecting corn in South Dakota. Jones (1968) considered the rootworm the number one corn pest in South Dakota and estimated that the rootworm caused fifty percent of all insect damage done to corn. Prior to 1961 the northern corn rootworm was the predominant species causing damage in South Dakota. The western corn rootworm is presently the predominant species (Nearman, 1968). Cultural and chemical control methods have been used to control corn rootworms in the past with varying degrees of success. Crop rotation, one of the first methods used (Forbes, 1915), has given some degree of control (Bigger, 1932). With the increase in land values in the late 1940s farming practices changed considerably. It became necessary to continuously place a high value crop such as corn on the best soil. Corn on corn then became the common practice. A rapid increase in corn rootworm populations coincided with these practices (Jessen, 1970). During this same period, following World War II, the feasibility of chemical control of corn rootworms was enhanced with the development of a new family of insecticides, the chlorinated hydrocarbons. From numerous tests in several states, aldrin and heptachlor became the recommended materials for corn rootworm control (Hill, Hixson and Muma, 1948), (Muma, Hill and Hixson, 1949), (Cox and Lilly, 1953), (Lilly, 1954), (Burkhardt, 1954), (Bigger and Blanchard, 1955), and (Apple, 1957). The economic damage to corn by the rootworms and the cost of control have been high. The estimated total loss to farmers in South Dakota in 1968 was seven million dollars (Jones, 1968). The estimated total loss in 1969 was also seven million dollars (P.A. Jones, personal communication). Although the loss attributed to rootworms has been high, the savings from use of recommended insecticides must be considered. In 1968, over 1,100,000 acres of corn were treated with rootworm insecticides. South Dakota farmers realized a savings of 800,000 bushels of corn above the cost of treatment. In 1969, an estimated 900,000 acres of corn were treated with corn rootworm insecticides. This treatment saved 1,500,000 bushels of corn above the cost of treatment (B.H. Kantack, personal communication). Chlorinated hydrocarbon insecticides were used extensively until the early 1960s, when failures of aldrin and heptachlor occurred (Weekman, 1961). Other groups of insecticides including organophosphates and carbamates were tested and subsequently recommended. Ball and Weekman (1962) tested and recommended two organophosphates, diazinon and phorate, for use of corn rootworms. With the subsequent use of large amounts of organophosphates the possibility of resistance comparable to that of the chlorinated hydrocarbons was anticipated. Ball (1968) reported a trend to resistance of corn rootworms to diazinon and phorate in Nebraska. The study reported in this thesis was initiated in the summer of 1969 as a test model for an annual monitoring system of most rootworm insecticides used in South Dakota. The primary objective was to determine the LD50’s of the recommended rootworm insecticides on western corn rootworm adults collected each year from several sites in the more intensive corn growing areas of the State. Comparison of the yearly LD50’s should disclose if a trend towards resistance exists. Only adults were used in this study since larvae were very difficult to collect from the field in any number and rearing techniques were time consuming and unsure. From tests which compared LD50’s on larvae and adults, it has been concluded that if the adults were resistant the larvae were also resistant (Hamilton, 1966), (Brazzel, 1970).

Library of Congress Subject Headings

Corn -- Diseases and pests
Corn root rot

Format

application/pdf

Number of Pages

46

Publisher

South Dakota State University

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Included in

Entomology Commons

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