Are significant multi-colored Asian lady beetle, lacewings, minute pirate bugs, parasitic wasp populations and fungal pathogens keeping soybean aphid populations in check? We spotted soybean aphids at relatively low levels in a soybean plot at a field day last week. After checking several other fields, I am curious as to whether or not our natural predators are naturally limiting the populations of the pest below economic threshold levels.

We are aware of some fields being treated in Ohio, with levels in most fields. As of this writing (Thursday, Aug. 18), soybean aphid populations we have observed are below threshold, but are noticeable and rising. Farmers should consider scouting their fields for the remainder of the summer. While we cannot predict whether any area or field will have populations reaching threshold, the possibility exists.

Ohio State University Extension Entomologists Ron Hammond and Andy Michel stated in a recent CORN Newsletter to remember that the threshold for spraying is an average of 250 aphids per plant with a rising population (http://ohioline.osu.edu/ent-fact/pdf/0037.pdf ). This is the threshold for taking action, not the economic injury levels which is in the vicinity of 700-900 aphids per plant. So there is no need to spray prior to an average of 250 aphids per plant.

Note: Any insecticide application prior to reaching economic threshold levels will destroy all beneficial insects, which may result in a retreatment later in the season.

A sampling procedure called speed scouting was developed at the University of Minnesota several years ago. This method suggests that when most of the plants have over 40 aphids per plant (e.g., 11 of 11 randomly sampled plants all have over 40 aphids per plant without any plants having below that number), treatment is warranted. In speed scouting, it is suggested that you should sample twice within 3-4 days, making a treatment decision each time, before actually making the choice to treat. For more information on soybean aphid speed scouting, see the following two web sites out of Iowa State University for a speed scouting brochure and video, respectively: www.iasoybeans.com/productionresearch/publications/aphid card/aphidcard.pdf and www.plantmanagementnetwork.org/edcenter/seminars/AphidSpeedScouting

The best visual guide I have found for estimating soybean aphid populations was produced by the Integrated Pest Management Program (IPM) at the University of Wisconsin-Madison. We have a number of printed cards available at Extension offices in Ohio but anyone can download a copy at http://ipcm.wihttp://ipcm.wisc.edu/Publications/tabid/54/Default.aspx

Excellent color photos provide a visual guide to the number of soybean aphids per leaflet. Four photos depicting 30, 60, 120 and 300 aphids make it easy to estimate aphid levels. Of course, soybean aphid count will vary from leaflet to leaflet. The guide recommends adding up the total number of aphids on the entire plant, not on a single leaflet. Then, to calculate a field average, count the number of aphids on 20-30 plants per field.

In dry areas, two spotted spider mites are still being found and should be watched closely. Fortunately for most, periodic showers (although light), morning dews and daytime humidity has kept most mite populations relatively low. In addition, the various soybean defoliators that occur each summer are being found and warrant watching, including Japanese beetles, Mexican beetles, bean leaf beetles, and grasshoppers. See our web site at http://entomology.osu.edu/ag/ for information on all of these pests.
Finally, please remember guidelines for protecting honeybees when applying insecticides to soybean.

According to Ohio law, if a pesticide is toxic to bees, it is the applicator’s responsibility to contact the beekeepers with registered apiaries (beehives) within a half mile of the target area if it is more than a half acre in size and the crop is in flower.

Contact the Ohio Department of Agriculture for more information on apiaries in your area.

The views and opinions expressed in this column are those of the author and not necessarily those of Farm World. Readers with questions or comments for Roger Bender may write to him in care of this publication.