By Janet J. Knodel
Extension Entomologist
Some “hotspots” soybean fields are at economic threshold (E.T. = average of 250 aphids per plant, 80% of the plants infested, and increasing populations) and will be or have been sprayed with insecticide for soybean aphid control. These fields are located near the Red River Valley area (see maps). We also are just starting to see soybean aphids in other outlier areas – Pembina and Rolette in NE, and Wells and Benson Counties in Central North Dakota. Ninety three fields were scouted by the IPM Scouts for soybean aphids last week. The IPM scouts in North Dakota and Minnesota found soybean aphids in 55% of the soybean fields surveyed. Percentage of plants infested with soybean aphids ranged from 0 to 100% with an average of 51% of plants infested, an increase from last week’s average of 39%. The average number of soybean aphids per plant ranged from 1 to 225. Our high count last week was only an average of 67 aphids per plant, so aphid populations are increasing. We are and will continue to get migratory winged aphids from neighboring states through the fall, so scouting is the best way to find and identify any fields above E.T. Scouting also is very important as the soybeans are in the susceptible reproductive stages. The USDA NASS reports that 71% of the soybeans were blooming (R1), and 23% setting pods in North Dakota (USDA NASS News Release – July 20, 2015).
