Soybean Aphids in Area Fields
Most all soybean fields in Northwest Missouri have soybean aphid populations. The economic threshold is 250 aphids per plant and this includes a window for treatment. This means that one should not treat when there are less than 250 aphids per plant. The threshold has a treatment time window included which allows you plenty of time to control the pest before they reach the economic injury level.
Check soybean fields now as the cooler temperatures are ideal for rapid increase aphid populations. Aphids have many generations per year and prefer the cooler temperatures we are receiving. Aphid populations can double in less than a week when temperatures are ideal.
My colleague to the north, Kyle Jensen, ISU Extension Field Agronomist located in Southwest Iowa, reported a border effect and advises growers to walk in at least 100 feet from the edge.
When we scout for this insect, carefully look under leaves and on stems of the soybean plants. I like to pull a plant so I can see the aphids easily and get my eyes acclimated to looking at this pest. This in turn will help you as you examine other plants.
As far as insecticide control, many products work equally. If you sprayed early season, you may have knocked out the beneficial insects and some products have repellency characteristics which keep the beneficial insects from moving back into the field. In these situations, be sure to watch these fields as beneficial insects generally keep aphid populations in check in our area. You may find populations increase dramatically in these early treated fields.
For more information contact Wayne Flanary, University of Missouri Extension Agronomy Specialist at 660-446-3724 or Heather Benedict, Agronomy Specialist at 660-425-6434 located in the Harrison County Extension office at Bethany.
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