No. 16 Article 5/July 11, 2008

Soybean Aphid Situation

There's not much threatening about soybean aphids throughout most of the Midwest this year, although recent increases in some areas bear watching. David Ragsdale, research/extension entomologist at the University of Minnesota, reported that soybean aphids had exceeded the economic threshold of 250 per plant in one early-planted, river-bottom field in Minnesota, but numbers elsewhere have been very low. Russell Higgins, University of Illinois Extension IPM educator in Morris, found soybean aphids on 5 of 20 plants he examined in his soybean rust sentinel plot in early July. The numbers of aphids he found on the five plants were 5, 8, 4, 9, and 178. Okay, that last number will catch your attention. Russ observed what appeared to be Syrphid fly larvae (flower fly larvae) preying on some of the aphids. Other predators, parasitoids, and pathogens also may yet take their toll on resident aphid populations. Nonetheless, temperatures between 70°F and 86°F will encourage rapid development of aphid populations, which can double in size in 3 to 4 days.

We soon will regularly post to a Web site the numbers of soybean aphids being found in 26 commercial soybean fields in Bureau, Lee, Marshall, Putnam, Ogle, Stephenson, Whiteside, and Woodford counties, a survey supported by funding from the Illinois Soybean Association. Look for more information in a near-future issue of the Bulletin.--Kevin Steffey

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