August 13, 2008
Soybean aphid numbers have exploded in some fields. The cool weather is ideal for aphids, and populations have been doubling every 2-3 days. There are a number of fields over the economic threshold of 250 aphids per plant, especially in the northern part of the area. Later planted fields appear to have larger numbers of aphids. In some years the aphid numbers have declined rapidly after Aug 15-20, but I don’t think we can count on that this year with the later than normal maturity of the soybeans and cool weather. I have seen very few aphid predators this year, which may partially explain why populations are building so rapidly. Some insecticide trial results can be found at http://www.ipm.iastate.edu/ipm/icm/2006/1-23/insecticide.html. Remember to check the pre-harvest intervals on the label for any insecticides used.
One alternative for scouting is to use the “speed scouting” method developed at the University of Minnesota. You only have to be able to count to 40 to use this method, but need to take a spreadsheet to the field to take notes and make a decision. The following site describes the method and provides a link to download the spreadsheet. http://www.soybeans.umn.edu/crop/insects/aphid/aphid_sampling.htm
FOR YOUR CALENDAR
Nitrogen Management Tour
Wednesday, August 20 5:30 p.m.
Bob McArthur Farm – Whittier
Iowa State University Extension and Linn Co-op will be presenting a tour on the Bob McArthur farm just west of Whittier the evening of Aug. 20. Many rates, sources, and timings of nitrogen fertilizer are being investigated on the farm. Dr. John Sawyer, ISU Extension Agronomist – Soil Fertility, will be discussing advances in nitrogen management at the tour. A free meal will be available at 5:30 p.m., followed by the tour. Please call the Linn CO-OP by August 15 at 854-6192 or 1-800-747-2616 to reserve a meal.
Fall Field Day
SE IA Research & Demonstration Farm – Crawfordsville
Wednesday, September 10
More Details will follow.
If you have any questions, please feel free to contact the Iowa State University Extension Office.
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