Soybean Producers Should Begin Looking in Fields for Soybean Aphid

North Dakota State University -- NDSU Agriculture Communication
7 Morrill Hall, Fargo ND, 58105-5655, Tel: 701-231-7881, Fax: 701-231-7044
agcomm@ndsuext.nodak.edu

July 3, 2002

Soybean Producers Should Begin Looking in Fields for Soybean Aphid

North Dakota soybean producers are at the point in the season where they need to check their fields for the presence of soybean aphids. Those who aren’t looking for soybean aphids now could be facing significant yield losses, according to a North Dakota State University entomologist.

There have been reports of soybean aphids in the Wahpeton and Fairmount areas of Richland county. Aphids have also been found in Grant and Stevens Counties in Minnesota. So far, the aphid numbers in these sightings are not at treatment levels.

"It is critical that producers are in the fields scouting for the aphids and deciding if treatment will be necessary," says Phillip Glogoza NDSU Extension Service entomologist. "By checking fields before significant infestations develop, growers and consultants should be able to make timely decisions on whether to treat."

Soybean aphid was originally discovered in the United States in 2000, when it was found feeding on soybeans in Michigan, Illinois, Wisconsin, Iowa and southeastern Minnesota. It spread to the eastern counties of North Dakota in the 2001 season. There were no economic infestations but there is great potential for yield losses in 2002, Glogoza says.

He reports that the aphids are found on the top portion of the plant and the colonies will form on the underside of the leaves. The aphids are small soft-bodied insects and may be winged or wingless. They are light yellow with black coronicles ("tail-pipes") and a pale colored cauda (tail projection). Winged adults will have a black head and thorax and in mid August the aphids are lighter in color.

According to Glogoza, there may be significant damage caused by the aphids. In Minnesota and Wisconsin losses ranging from 0 to 17 bushels per acre were reported in 2001 from untreated plots. The aphids suck sap from the plants and infested leaves will wilt and curl. Other symptoms of direct feeding are plant stunting, reduced pod and seed counts, puckering and yellowing of the leaves. They are also capable of transmitting viruses which include alfalfa mosaic, soybean mosaic and bean yellow mosaic.

"Treatment to manage soybean aphids would be recommended at early flowering when aphids are abundant on most plants," Glogoza says. "Our best guideline for defining abundant is when aphids are averaging 25 or more per leaflet."

Flowering and early pod fills are critical times for aphid control. Large numbers of aphids feeding on soybeans may cause flowers and pods to abort. Spraying later in the season after pods are formed maybe too late to gain yield equal to the cost of treatment, Glogoza reports.

A field checking strategy for making treatment decisions uses a rating scale of zero to four to evaluate individual leaflets, says Glogoza. For more information on the rating scale see the publication produced by the NDSU Extension Service, "Soybean Aphid, Management in North Dakota," E-1232. The publication is available at county extension offices of the NDSU Extension Service and on the web at www.ext.nodak.edu/extpubs/plantsci/pests/1232w.htm. In general if there are more than 25 aphids in a sample leaflet treatment should be used. Glogoza gives a checklist of things to consider when deciding to spray.

Aphid number -Leaflet rating of at least 3.0 or average 25 or more aphids per leaflet.

Aphid appearance -Aphids are healthy and fungus-infected aphids not present.

Plant appearance -Honeydew present on the leaves is a sign that aphid numbers are large.

Timing -Early reproductive stages are when the greatest benefit from control occurs.

Weather conditions -If dry, fungal infections that control the aphid will be low.

Plant stage -Flowering and early pod fill are critical times.

"July is probably the most beneficial time to treat aphids. June is too early to make a spray decision and August may be getting too late to get the most yield advantage from treatment, thus the importance of producers to begin scouting fields now," Glogoza says.

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Source: Phillip Glogoza, (701) 231-7581, pglogoza@ndsuext.nodak.edu
Writer: Stephanie Renner, (701) 231-8371, Stephanie.Renner@ndsu.nodak.edu
Editor: Tom Jirik, (701) 231-9629, tjirik@ndsuext.nodak.edu