No. 15 Article 5/July 1, 2005

Update--Soybean Aphids

Our surveillance of soybean fields, primarily in northern Illinois, continues. Fortunately, there's not much new to report this week. The high temperatures seem to have suppressed development of soybean aphid colonies, because the numbers of aphids our crew found on June 27 and 28 did not increase from the week of June 20 to the week of June 27. The guys surveyed 19 fields in the following 11 counties in central and north-central Illinois: Bureau, DeKalb, Ford, LaSalle, Lee, Livingston, Marshall, McLean, Ogle, Putnam, and Woodford. The surveyors found no soybean aphids in 9 of the 19 fields surveyed; the average number of soybean aphids per plant in fields in which they found soybean aphids ranged from 0.09 to 11.18. They found soybean aphids in almost all of the northernmost counties (Bureau, DeKalb, LaSalle, Lee, Ogle, Putnam) and very few to no aphids in the southernmost counties. One field of soybeans in Ogle County had an average of 11.18 soybean aphids per plant, with a range of 0 to 29 aphids on individual plants. They found soybean aphids on 10 of the 11 plants examined, and lady beetles were present in the field.

We have not heard many shouts about threatening levels of soybean aphids from our neighboring states, although numbers are increasing at a steadier pace in Michigan, Minnesota, and Wisconsin.

So, with all of the other insect (and mite) activity occurring in our soybean fields and cornfields, at least we don't need to worry much about soybean aphids--for now. Don't let your guard down, however. We still don't know exactly how soybean aphids will respond to high temperatures in North America, but we'll soon have a good idea if our weather continues as is. Also, a return to lower temperatures (75-85°F) will benefit the soybean aphids already present in soybean fields. Keep scouting to avoid surprises.--Kevin Steffey

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