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Soybean Yield Reports Coming In

November 6, 2003

With the conclusion of harvest, we draw closer to closing the book on the 2003 soybean aphid outbreak. This past summer, populations of soybean aphids reached extremely high densities. With the threat of yield reduction, many growers used insecticides in an attempt to manage this pest. Based on information obtained from several members of the Illinois Agricultural Aviation Association, we estimate that 750,000 to 1 million soybean acres were treated aerially for control of soybean aphids in Illinois in 2003.

We are just now getting a glimpse of yield loss experienced by producers throughout Illinois. As of November 2, the Illinois Agricultural Statistics Service reports that 95% of soybeans have been harvested in Illinois. In the October report, the United States Department of Agriculture forecasted a soybean yield of 34 bushels per acre for Illinois (383 million bushels in Illinois), 6 bushels per acre less than the 2002 average. Although damage caused by the soybean aphid may include a reduction of pods per plant and seed weight, we cannot assume that these low yields are due entirely to the soybean aphid. As we analyze the yields this fall, we need to remember that dry weather conditions and disease most certainly affected plant health and development as well.

Last month we asked you to complete a report form to help us learn more about the effects of the soybean aphid on yield, and we've received several responses. Let's start off by thanking those who have submitted yield data thus far. We appreciate your help!

Table 1 and Table 2 provide a summary of the yield data we have received from 16 different fields, representing eight counties in Illinois. Three different products were used in these fields: Lorsban 4E, Mustang Max, and Warrior. Dates of insecticide application ranged from the end of July through mid-August. Just as with reports across the state, soybean yields reported here were quite variable. Yields of treated fields had a range of 27.5 to 61.6 bushels per acre (average 48.6 bushels per acre), and untreated areas of fields had a range of 20.8 to 42.8 bushels per acre (average 36.1 bushels per acre). The average difference be-tween yield of treated soybeans and yield of untreated soybeans was 12.5 bushels per acre.

We are still requesting submission of yield data. Please use this form to submit your information for individual fields or trials. You may not be able to supply all of the information listed, but don't let that prevent you from filling in what you do know. Any information you can supply will be helpful! If we receive some more useful responses, we will summarize the additional information and publish it in the next issue of the Bulletin. As before, anonymity of individuals who submit information will be retained in any articles we write.

Please mail or fax responses to Kevin Steffey, Mike Gray, or Kelly Cook at Department of Crop Sciences, Turner Hall, MC 046, 1102 S. Goodwin Ave., Urbana, IL 61801; fax: (217)333-5245.

Responses also may be sent electronically to,, or Please copy the form from the Web into a word-processing (Word or WordPer-fect) document and complete the form. Attach the completed form to an e-mail message. Please address any questions to Kevin Steffey, Mike Gray, or Kelly Cook, (217)333-6652.--Kelly Cook, Kevin Steffey, and Mike Gray

Author: Mike Gray Kevin Steffey Kelly Cook

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

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