A larval damage prediction method for Diabrotica virgifera virgifera LeConte was evaluated in west central and northeastern Nebraska from 1978–1980. Cornfields averaging < 1 beetle per plant during every weekly count in August were considered to have little chance of being economically damaged by larvae the next year and treatments with soil insecticide were not recommended. Fields averaging > 1 beetle per plant on any sampling date were considered to be indeterminant with respect to a damage prediction; the growers were advised to use a soil insecticide as a precautionary measure. With the possible exception of a few fields in northeastern Nebraska, in which yield difference probably was not due to D. virgifera virgifera larval feeding, the prediction method was reliable >80% of the time. The study indicated that lowering the treatment threshold to 0.75 or 0.90 beetles per plant increased the prediction accuracy to >90% (root damage ratings <2.75), with none of the fields with prediction errors being seriously damaged (root damage ratings <3.1). As a result of this study, only 158 and 263 of ca. 3,050 ha of field corn in the west central study area were treated with soil insecticide for D. virgifera virgifera in 1981 and 1982, respectively. No serious problems were reported in the untreated fields by the field scouts. Before the IPM program, ca. 90%of the fields were treated with corn rootworm larvicides.
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Stamm et al. (1985) studied this question.