By Robert Koch, Bruce Potter
Soybean aphid populations have been generally low across Minnesota. However, populations in some fields in southwest and southeast Minnesota are nearing threshold levels and may require insecticide application to protect yield. In these areas, soybean aphid infestation levels very considerably from field to field, so you should rely on scouting and the economic threshold (80% or more of the plants with aphids, average of 250 aphids per plant, aphid numbers increasing) to determine when to apply insecticides for soybean aphid.
As folks consider spraying fields for soybean aphid, we want to remind everyone that soybean aphid has developed resistance to pyrethroid (Group 3A) insecticides. Currently, any populations of soybean aphid in Minnesota should be considered potentially resistant to pyrethroids. Insecticide rotations are an important part of insecticide resistance management and may help reduce the chances of further development of insecticide resistance in soybean aphid. If a field needs to be sprayed more than once, it is important to rotate to a different insecticide group for the follow-up spray. On a
new webpage, we provide some guidance for insecticide rotations for pyrethroid-resistant soybean aphid: