No. 23 Article 1/October 8, 2010

Soybean Aphid Fall Migrants Finding Buckthorn Plants Despite Low Aphid Numbers

The growing season of 2010 will be remembered for many reasons, including the fast-paced planting of corn, the hot summer, the early harvest, low numbers of western corn rootworms and Japanese beetles, and the lack of significant infestations of soybean aphids. Many of us will recall the swarms of soybean aphids in late summer and early fall in 2009, especially across central and southern Illinois. Those large densities of fall migrants that made their way to their overwintering host, buckthorn, were eventually killed by a fungal epizootic that swept through the population. Overcrowding of aphids on buckthorn leaves facilitated the efficiency of this disease. As a result of this epizootic, very few soybean aphids survived the winter of 2009-10, and producers were fortunate to have exceedingly low densities of this pest in their fields throughout the growing season. The unusually hot summer also kept infestations at non-economic levels. Entomologists in several north-central states likewise reported low numbers of soybean aphids.

Despite these low densities, David Voegtlin, a retired Illinois Natural History Survey entomologist, has recently observed small numbers of aphids on buckthorn plants growing on the University of Illinois campus. No aphid predators were observed on these plants. Dave and I are both amazed at the ability of these winged aphids, in spite of their low numbers, to locate buckthorn plants. Crowding on buckthorn leaves will not be an issue this fall.

It is too early to predict what 2011 will bring with regard to aphid infestations. The severity of the winter, soybean planting dates in 2011, and summer temperatures are all factors that will influence aphid densities during the next growing season.--Mike Gray

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