By Scout Nelson
Soybean aphid populations are increasing in some Minnesota fields as summer temperatures become more moderate. Earlier heat helped slow aphid growth, but recent conditions are creating better opportunities for populations to increase. Dry areas may also face pressure from two-spotted spider mites.
Robert Koch, Extension Soybean Entomologist, and Eric Yu, Extension Educator – IPM Crops, emphasize the importance of continued field scouting and careful pest management as soybeans approach maturity.
Farmers should base scouting decisions on soybean growth stages rather than calendar dates. Fields should be checked at least once a week through early R6.
Late planted and less mature fields may remain attractive to soybean aphids for a longer period. Farmers should inspect the entire plant, including lower leaves, stems, branches, and pods.
Live adult aphids, nymphs and small light-colored aphids should be counted. Dead aphids, shed skins, parasitized aphids, and insects that look similar to aphids should not be included.
Through the R5 stage, the economic threshold is an average of 250 aphids per plant, with more than 80% of plants infested and populations increasing. Fields below this level should continue to be monitored instead of receiving unnecessary insecticide treatments.
There is no formal economic threshold for R6 soybeans. Very high populations may still reduce yield during early R6, especially when plants face environmental stress. Decisions should be made based on field conditions.
Farmers should avoid treating fields when aphid populations are clearly declining. Natural enemies, weather, and soybean maturity can cause populations to fall naturally.
When treatment is needed, growers should check preharvest intervals and insecticide labels. Pyrethroid resistance is widespread in Minnesota, so standalone pyrethroid products should be avoided for aphid control.
Selective products containing sulfoxaflor, afidopyropen or flupyradifurone may offer effective control while protecting beneficial insects.
Hot, dry weather can also increase spider mite problems. Some pyrethroids can worsen mite outbreaks, so both pests should be considered before treatment.
Photo Credit: gettyimages-gilaxia
Categories: Minnesota, Crops, Soybeans