April- June 2002
Brian J. Lang , ISU Extension Field Specialist/Crops
A largely unknown, newly introduced insect pest, the Soybean Aphid, appeared in northeast Iowa soybean fields in 2001. No research on this pest existed on predictions of potential damage, economic threshold levels, or methods of control. Most agricultural providers and farmers ignored the pest since little was known about it.
I noticed the presence of the insect early in the season on May 18. Since little was known of the insect, ISU Extension cooperated with a local farmer to establish plots to monitor the potential of the pest on soybeans. Plots were monitored weekly, collecting information on the spread of the insect, its change in population, noticeable stress on the soybeans and the presence of beneficial predators. As the population advanced, insecticide trials were established on July 12 to further monitor the control of the insect and determine if one insecticide worked better then another.
Within a week of establishing the insecticide trials, the insecticide treatments were relieving stress on the soybeans caused by the high populations of Soybean Aphid. While no research on this pest existed to support these observations, the data collected on these plots supported “best guess” recommendations for farmers to treat this potential problem now, before additional stress by the insect robbed more yield from the farmers' soybean crop.
Starting July 19, and for the next week, announcements were made on email, radio, local newspapers and through field events to educate farmers and agricultural providers on what Extension uncovered about this insect. With these events, ISU Extension contacted over 500 farmers and 30 agricultural providers in northeast Iowa . Farmers and agricultural providers proceeded to treat approximately 35,000 acres of soybeans infested with this insect.
End of season yield checks of ISU Extension plots, and additional yield checks from some of the agricultural providers treated fields at the encouragement of Extension, provided evidence as to the success of the efforts. On average, soybean aphids caused a 20% yield reduction where it was not treated with an insecticide. The average net return to insecticide treatments was $30 per acre. For the 35,000 acres treated, this meant that farmers salvaged over $1 million in net profit with their quick response to the soybean aphid problem once the potential problem was realized by insightful action of ISU Extension.
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