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Soybean Aphid Thresholds

Soybean aphids are tiny, soft-bodied insects that pierce a plant and feed on the sap. They reproduce rapidly and in large enough numbers, aphids can reduce yield and quality. Soybeans are susceptible to aphid injury till the crop reaches full seed.

Bruce Potter is an extension integrated pest management specialist with the University of Minnesota. He says not every field is going to have aphids, and infestation levels can even vary within a field.  When you’re out scouting, sample at least 20-to-30 plants per field.

"What I always do is pull them out of the ground, turn them over, the aphids tend to be on the bottom of the leaf. Look at those leaves and if you’re averaging over 250 per plant, that’s kind of the treatment level," says Potter. " 250 aphids per plant on an average does not look like much at all, there’s not going to be plants dripping with honeydew, or anything like that."

Potter says to also weigh the economic injury level with the economic threshold.

"The economic threshold, that 250 aphids per plant, that’s way ahead of where any kind of yield loss happens. And even if populations are increasing fairly rapidly, you’ve got a least a week in there to get those treatments on before you have any chance of losing any money," he says. "So, again, the threshold is where you want to stop the problem from increasing, the economic injury level is where you’re actually having some economic loss."

He says to use insecticides judiciously, especially pyrethroids. Aphids have found a way to outsmart the system so only treat the areas that need treating.