Efficacy of intercropping in organic soybeans for management of the soybean aphid

Graduate Student: Thelma Heidel, University of Minnesota Department of Entomology

Major Professor: Dr. George Heimpel, University of Minnesota Department of Entomology

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Organic soybean producers lack effective management options for controlling the economically damaging soybean aphid, Aphis glycines Matsumura. Biological control by natural enemies is an important control measure in organic agricultural systems, and intercropping with flowering crops such as buckwheat can enhance biological control by attracting natural enemies. The purpose of this research project was to investigate whether intercropping organic soybeans with buckwheat can be an effective management option for suppressing soybean aphid populations. In 2010 and 2011 field experiments were conducted in Minnesota to investigate 1) whether a soybean/buckwheat intercrop could effectively manage soybean aphid populations and 2) if so, whether natural enemy recruitment was a mechanism involved. Comparisons between intercropped plots and soybean-only plots showed slight differences between aphid and natural enemy numbers for all locations, however none of these differences were statistically significant. While natural enemy populations did follow fluctuations in aphid numbers over the season, the natural enemies contributing toward biological control did not exhibit a strong positive response to the presence of buckwheat in this study. Since aphid populations did not decrease due to the presence of buckwheat, there is little evidence that natural enemy recruitment is occurring in this system. Soybean aphid populations in both sample years were relatively low, and both years barely exceeded the economic threshold of 250 aphids/plant before early August. Further aphid suppression measures beyond naturally occurring biological control would not have been recommended in either year.

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