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Scouting fields for soybean aphids


Fri, Aug 13th, 2010
Posted in Agriculture

While many of us were enjoying the Fillmore County Fair, the summer crew from the Extension Regional Office, working with regional crop Extension Educator Lisa Behnken, Ryan Miller, and IPM Specialist Fritz Breitenbach, were out scouting for soybean aphids. Listed below are some of their thoughts and observations:

Soybean aphids (SBA) continue to be present at very low densities in the fields we are monitoring. We are finding very few winged adults at this time. At this juncture in time it is a very real possibility that SBA may be a non issue in SE Minnesota. No, that doesn't mean you can stop scouting, however, you may wish to refocus your efforts.

Fields to watch: Late-planted fields (especially beans after peas), no-till fields, low fertility fields, soybean fields which received an insecticide application earlier in the summer and last, but not least, drought stressed fields. By the first week in August we should have a better handle on what is going on and what we can expect for the rest of August.

The Economic Threshold Number = 250 aphids/plant on 80 percent of soybean plants and the population is increasing. Remember-The economic threshold number of 250/plant is well below the number/plant that results in economic injury.

We are closely monitoring three fields in SE Minnesota as of July 19, 2010; our Houston county field had an average aphid count of 0.95 SBA per plant with 45 percent of the plants infested. Our Goodhue County field had an average of 9 SBA per plant with 90 percent of the plants infested. Our Olmsted county field had an average of 13 SBA per plant with 90 percent of the plants infested. The Olmsted county field typically runs high and has been a good indicator field in the past.

Okay, it is time for the disclaimer: There is no way that three fields can accurately mirror what is going on in your field! You still have to scout your fields to know what is happening.

We still have roughly 33 days where the 250 aphids per plant threshold works. Yield loss from SBA during the R6 stage is still a possibility; however, SBA populations would need to be at a very high level. Unfortunately, there is not a large enough research base to determine what that number is. We have the prospect for an above average soybean crop in SE MN. Let's do everything we can to keep it that way.

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