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Posted 15 September 2008. PMN Crop News.

Scout for Soybean Aphids

University of Illinois at Urbana-Champaign.

Urbana-Champaign, Illinois (September 1, 2008)--Mike Roegge, Crops Educator, University of Illinois Extension, Adams/Brown Unit, reports that the cool weather being enjoyed of late has not really benefited crops to any great degree. Nor has it helped in terms of soybean aphids, which actually benefit from these temperatures. So far this summer, there have only been 3 days in which the temperature exceeded 90 degrees. And while this sure helps on reducing the AC bill, late planted crops sure would appreciate some warmer weather, especially the soybean crop.


You need to be scouting soybean fields for soybean aphids. An increase in population in some fields has been noticed over the past week or so. Soybean aphids have been present for almost a month now, but populations were kept in check. However, the cooler temps have allowed the aphids to thrive.

Thresholds for aphid control are 250 aphids per plant. Which is the same threshold as always. Even though soybean prices are twice what they were the last time aphids were seen, the threshold remains the same. The reason is the economic injury level is close to 450 aphids per plant. The difference between these two numbers is to allow time for control to be lined up and applications to be made.

Now it's not easy counting 250 individual aphids, so "cheat sheets" have been developed to help. The University of MN has developed a speed scouting guide that may benefit growers. It is available at the following website:

Remember that most recommend control of soybean aphid until the R6 stage of soybean growth. This stage of growth is reached when the pod at one of the 4 uppermost nodes contains full sized green beans.

University of Illinois Extension provides equal opportunities in programs and employment. Extension programs and materials are research based and strive to meet the needs of people locally. If you need a reasonable accommodation to participate in this program, contact Rick Keim at 217-942-6996.

Mike Roegge
Unit Educator, Crop Systems