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Soybean Aphids--Increased Densities in Northern Illinois Compared with Previous Two Years

July 2, 2003

Although it's still too early to predict accurately the severity of soybean aphid infestations this year, recent observations in northern Illinois suggest that growers will need to be vigilant with respect to this insect pest for the remainder of the season. David Onstad, an entomologist with the Department of Natural Resources and Environmental Sciences, shared these data for Kendall County: number of soybean fields infested (14 fields were sampled) in 2001, 2002, and 2003--8, 8, and 14, respectively; average number of plants (50 plants sampled) infested per field in 2001, 2002, and 2003--2.14, 1.57, and 14.3, respectively; and average number of aphids per plant in 2001, 2002, and 2003--1.57, 0.19, and 3.44, respectively. In 2001 and 2002, sampling was conducted in early July. In 2003, sampling was performed on June 24. So even though soybean fields were scouted earlier this year for soybean aphids, 100% of the fields examined were infested. In addition, nearly 29% of the plants were infested. This compares with slightly more than 3% of plants infested in early July 2002. Thus far, we have not received many reports of soybean aphid infestations. If aphid numbers begin to increase rapidly in your area, please let us know so that we can pass along the information to our readers. For now, stay tuned; the soybean aphid story is yet to be written for 2003. Natural enemies and weather may take their toll on this insect pest as the season develops.--Mike Gray

Author: Mike Gray

The Pest Management and Crop Development Bulletin
Executive Editor: Kevin Steffey, Extension Entomologist

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