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NEW SOYBEAN PEST APPEARS IN THE MIDWEST: IS IT IN MINNESOTA??
Special Web Version: Late-Breaking News

Since its introduction in the U.S., soybean has been free of some of the pests that haunt it in eastern Asia and Australia, particularly aphids. However, our aphid-free days appear to be over. Chris Difonzo, extension entomologist in Michigan and John Wedberg, extension entomologist from Wisconsin, recently reported aphids infesting soybean in Wisconsin, Michigan and northern Illinois. On August 15, the aphid was positively identified as the soybean aphid, Aphis glycines Matsamura, which infests soybean in China, other east Asian countries and Australia.

Today, Bill Hutchison and Eric Burkness, St. Paul campus and Rosemount (Dakota Co.), respectively, found what appear to be "light" infestations of the same aphid (ID pending) on pod-filling soybeans (not yet senescing). These infestations range from 2/20 plants infested (St. Paul) to 3/70 plants infested (Rosemount). Mark Abrahamson, with MDA Crop Survey Group, is coordinating a state-wide effort to augment aphid surveys over the coming week. We would also appreciate your help in surveying Minnesota soybean fields (suggested protocol below).

What is the soybean aphid? The soybean aphid is a small yellow-green to green aphid (adults are pinhead size, with nymphs even smaller - much smaller than pea aphid or corn leaf aphid) with a pair of dark cornicles (abdominal "tail-pipe" projections) and a light cauda (tail projections). The aphid may be found on soybean stems, young developing leaves (earlier in the season) and, later in the season, under leaves in the middle of the canopy. Any aphid found feeding on soybean is likely to be the soybean aphid. (SEE Photo/Fact Sheet Web page addresses below). Should vegetable growers be concerned? For Snap and Lima Bean, Edible Bean, Growers: This aphid should be specific to soybean (and varieties within the Glycine genus); thus it should NOT be found on snap bean or dry edible bean (Phaseolus spp. or Vicia fabae).

Photos courtesy of Chris Difonzo, Michigan State University

What signs or symptoms do soybean aphids cause? Any aphid infestations produce "honey dew", the aphids attempt to excrete extra plant sap. Leaves with honey dew will glisten or take on a sooty appearance as molds grow on the plant sap. Light infestations may produce no visible symptoms. Plant symptoms under heavy infestations produce a yellowing reminiscent of potassium deficiency (see photo), cupping of leaves and may even stunt the plant. The most critical long-term concern is that this species is known to vector many serious virus diseases, including: soybean mosaic, and bean yellow mosaic. Unfortunately, many factors may cause yellowing in soybean. John Wedberg reports that populations are collapsing in Wisconsin, but even if aphid numbers have dropped, shed skins, honey dew and sooty mold can still verify the presence of aphids.

Are infestations worth treating with insecticide? Infestations of soybean aphid are probably not worth treating this late in the season. Soybean aphid infestations tend to peak on younger soybean and decline as soybean development shifts from vegetative to reproductive development. No economic thresholds are available. Severe infestations in both Michigan and Wisconsin were treated in late July and early August; however, John Wedberg reports widespread collapse of Wisconsin populations (in the absence of insecticide).

What should you do if aphids are present? Fields with aphids should be reported immediately to Ken Ostlie, extension entomologist for corn and soybean, via telephone (612-624-7436), fax (612-625-5299), or email (ostli001@tc.umn.edu ). Please include the following information:
1. Your name and contact information (address, office phone, cell phone)
2. Location of the field (county, township, section to nearest ¼, or GPS lat-long coordinates)
3. Farmer (operator)
4. Brief description of infestation, its position in field and on plants, and if plant symptoms are noted.

To provide more detailed information, consider the following protocol.
Sample at least 15 plants per field with plants located at least 15 paces apart. Look primarily at the UNDERSIDE of leaves in the top and mid-portion of the plants; also look at the main stem and petioles. Examine the entire plant for aphids, if you have time. Record the number of plants infested and rate the abundance of the infestation on each plant as follows: 1=light (only a few aphids present), 2=moderate (aphids common on plant), 3=heavy (plant inundated with aphids). Report % of plants infested (i.e., ONE or MORE present anywhere on the plant) and average rating.

NOTE: If winged aphids are present, collect aphids into a small plastic bottle containing alcohol (rubbing alcohol ok) with a paint brush.

Mail the sample to the following address:
Att: Allyson Milles
Department of Entomology
University of Minnesota
1980 Folwell Ave., Rm 219
St. Paul, MN 55108

Useful Websites, for more updates and info, by state:

WISCONSIN: Article by Dr. John Wedberg, University of Wisconsin, August 17, 2000
http://ipcm.wisc.edu/wcm/00-22insect1.html

ILLINOIS: Article by Dr. Mike Gray at the University of Illinois, August 16, 2000 http://www.ag.uiuc.edu/cespubs/pest/articles/200020h.html

FACT SHEET, Australia (Good photos and references) http://www.agric.nsw.gov.au/Hort/ascu/insects/aglycin.htm

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Last Revised August 22, 2000.
The University, including the Minnesota Extension Service, is an equal opportunity educator and employer.©1999 Minnesota Extension Service, University of Minnesota. All rights reserved. Contact copyright@extension.umn.edu for information on reproduction or use of this material.