By Jon Tollefson, Department of Entomology
After high numbers of soybean aphids last year, Iowa agriculturalists are beginning to ask the question, “Will 2009 also be an aphid outbreak year?”
Iowa State University entomologists working in soybeans have not seen enough aphid eggs on buckthorn to be alarmed. Remember, however, that aphid numbers will vary greatly from area to area and field to field. The variability in aphid numbers will not only depend on the overwintering success of aphids, but also reproduction on buckthorn in the spring, planting dates, the variety of soybeans planted, environmental conditions including temperature and rainfall, and the numbers of natural enemies.
Because there are good scouting techniques, accurate treatment thresholds, and effective therapeutic chemical treatments – the best management strategy for the soybean aphid is to scout soybean fields and only treat those that would benefit from an insecticide. An article published in the 2007 Integrated Crop Management newsletter gives a good overview of the soybean aphid.
An aphid sampling plan called speed scouting has been developed by University of Minnesota entomologists. An article that describes the technique can be found on a their Web site. Two pocket size references are also available from Iowa State University Extension and the Iowa Soybean Association - Speed Scouting Soybean Aphids, CS1 0015 and Soybean Aphid Field Guide, CS1 0011. These free publications are available from the Extension online store.
Throughout the summer, this newsletter will have announcements of aphids as they are found in Iowa. That will be the time to begin scouting your fields, and treating the fields that reach economic levels.
Treating soybean fields prophylactically, many of which may not have economic aphid populations, will worsen the conditions. The unnecessary insecticide treatments will kill natural enemies and the exposure to the aphids may promote insecticide resistance. Be patient. Scout. And stop increasing aphid densities in those fields where economic populations are reached.
Jon Tollefson is a professor of entomology with extension and research responsibilities. He can be contacted by email at firstname.lastname@example.org or by phone at 515-294-8044.