FIELD AND FORAGE CROPS Probability of Cost-Effective Management of Soybean Aphid (Hemiptera: Aphididae) in North America

Soybean aphid, Aphis glycinesMatsumura (Hemiptera: Aphididae), is one of the most damaging pests of soybean, Glycine max (L.) Merrill, in the midwestern United States and Canada. We compared three soybean aphid management techniques in three midwestern states (Iowa, Michigan, and Minnesota) for a 3-yr period (2005Ð2007). Management techniques included an untreated control, an insecticidal seed treatment, an insecticide fungicide tank-mix applied at ßowering (i.e., a prophylactic treatment), and an integrated pest management (IPM) treatment (i.e., an insecticide appliedbasedon aweekly scouting and aneconomic threshold). In 2005 and 2007,multiple locations experienced aphid population levels that exceeded the economic threshold, resulting in the application of the IPM treatment. Regardless of the timing of the application, all insecticide treatments reduced aphid populations compared with the untreated, and all treatments protected yield as compared with the untreated. Treatment efÞcacy and cost data were combined to compute the probability of a positive economic return. The IPM treatment had the highest probability of cost effectiveness, compared with the prophylactic tank-mix of fungicide and insecticide. The probability of surpassing the gain threshold was highest in the IPM treatment, regardless of the scouting cost assigned to the treatment (ranging from $0.00 to $19.76/ha). Our study further conÞrms that a single insecticide application can enhance the proÞtability of soybean production at risk of a soybean aphid outbreak if used within an IPM based system.