The southern corn rootworm is an annual soil insect pest of peanut in Virginia, North Carolina, Texas, and other peanut growing states. Larvae feed on developing pods causing direct yield loss and indirect damage by allowing entry of secondary pathogens. Because it is a soil pest, scouting is difficult and producers make preventive treatments without knowledge of actual pest abundance. In 1997, an index that predicts risk to rootworm damage on individual fields was released. The original index was validated using 44 commercial peanut field studies. In this paper the index was evaluated using 392 additional field case studies conducted in Virginia and North Carolina from 1997-2001. Factors influencing the index score (soil texture, soil drainage class, planting date, cultivar resistance, and field history of rootworm damage), and point assignments for predicting low, moderate, and high-risk fields were analyzed. The goal was to determine which combination of factors provided the highest percentage of correct risk predictions and minimal percentage of incorrect predictions. The best index combination, as with the original version, used all five factors to determine the total point score, with 70 or more points indicating a high-risk field, 55-65 points a moderate-risk field, and less than or equal to 50 points a low-risk field. Growers who use the index eliminate a preventive insecticide treatment in low-risk and some moderate-risk fields. From a practical perspective, using the index resulted in protecting fields from economic loss due to rootworm damage 98.5% of the time.
Species 1: Coleoptera Chrysomelidae Diabrotica undecimpunctata howardi (southern corn rootworm, spotted cucumber beetle)
Keywords: Risk Index
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