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I’m getting a lot of questions regarding treatment timing for soybean aphid. Mainly, when is it too late to treat? In the last week of August 2017, most fields are reaching R5/R6 and so the question is an important one. In my soybean aphid efficacy evaluation, I have sprayed at different plant growth stages to evaluate yield responses. I have never been able to demonstrate a yield response when spraying after R5.5. However, I would have to ask a few more questions before responding to a farmer:

1) how long have the aphids been there?

2) what other pests are present?

I recently posted an ICM News article about how scouting for alfalfa weevils in southern Iowa. It doesn't take too many accumulated degree days for them to start moving around and laying eggs. If you grow or scout alfalfa, you will likely see any adults that survived the winter moving in southern and central Iowa now and northern Iowa next week.

The last few weeks have been full of soybean aphid discussions. Populations have been going up, down and otherwise looked sort of bumpy this summer. Many fields exceeded the economic threshold of 250 per plant and were treated with foliar insecticides in August, particularly in northern Iowa. My lab had our big spray day last week, as aphid numbers approached the threshold. Of all the products we are using, we are seeing good efficacy, or knockdown, for soybean aphid. That is a good thing because aphids have historically become resistant to big classes of insecticides.