Wisconsin Crop Manager newsletter - Soybean Aphid Increasing and Variable

Soybean Aphid Increasing and Variable – Scout Fields Now

Jul 24

Posted by: WCM Staff
7/24/2008 2:50 PM

This week soybean aphid populations have increased noticeably. That is a relative term in this case. In some areas such as Dodge and Sauk Counties, this increase is from near zero activity to field averages of 10 aphids/plant and 30-60 aphids/plant. In other areas however, West Central and East Central Wisconsin for example, higher populations are starting to be reported closer to Economic Threshold in a few fields.

Soybean Aphid Increasing and Variable – Scout Fields Now

Eileen Cullen, Field Crop Extension Entomologist

Soybean Aphid Field Scouting Recommended: Overall, populations are still below economic threshold for WI. However, the population increases noted above are a reminder to remain alert and scout soybean fields. It’s been a quiet insect year thus far in field crops, but that can change quickly. Currently in Wisconsin, we are experiencing mild temperatures between 77 and 86° F. These temperatures are favorable for rapid soybean aphid increase. You may also be finding winged forms on plants as soybean aphids enter their summer migration phase. Scout fields regularly to detect any increase in soybean aphid population densities.

The soybean aphid Economic Threshold is 250 aphids/plant. This threshold is determined based on a field average calculated from 20-30 plants collected from throughout the soybean field. It is worth mentioning that the Economic Threshold is not the point at which soybean yield loss occurs (that is the Economic Injury Level). The Economic Threshold (ET) of 250 aphids/plant incorporates a 7 day lead time between treatment action and preventable yield loss.

Entomological research in six states (including WI) from 19 yield-loss experiments conducted over a 3-yr. period found no detectable yield differences attributed to treating soybean aphids at numbers below the Economic Threshold of 250/plant. Additionally, treating soybean aphids below the ET of 250 aphids/plant increases risk to producers by treating an aphid population that is growing too slowly to exceed the Economic Injury Level in 7 days, eliminates generalist predator insects, and exposes a larger portion of the soybean aphid population to selection by insecticides, which could lead to development of insecticide resistance (Journal of Economic Entomology 100: 1258-1267).

To learn more about the Soybean Aphid Economic Threshold, two presentations are available on the Plant Management Network. These presentations were made by Dr. David Ragsdale, Professor of Entomology at University of Minnesota. The first presentation covers the biological aspects of soybean aphid (reproduction, feeding habits, and its effects on soybean yield). The second presentation “Soybean Aphid: Economic Threshold and Economic Injury Level” discusses the points at which soybean aphid population densities go from benign to costly. http://www.plantmanagementnetwork.org/edcenter/seminars/SoybeanAphid/

Economic Threshold and Scouting Information

Please visit the UW Soybean Plant Health page for complete information on the economic threshold of 250 aphids per plant at R1-R5 soybean growth stages, and a guide to scouting http://www.plantpath.wisc.edu/soyhealth/aglycine.htm

Several soybean aphid publications are available at the Field Crop Extension entomology website. Please visit the URL below and scroll through the list of Extension publications: http://www.entomology.wisc.edu/cullenlab/site%20pages/extension/ext_pubs.html

Weekly Soybean Aphid Reports for WI on the ipmPIPE Website http://sba.ipmpipe.org

The Integrated Pest Management Pest Information Platform for Extension and Education (ipm PIPE) is a national portal for soybean aphid reporting in WI, regionally and nationally. Maps are updated weekly with soybean aphid densities from sentinel fields throughout WI accompanied by Extension specialist commentary and IPM recommendations for soybean aphid management. Information and soybean aphid reports are shared across the north central, eastern and southern region.

Visit the Soybean Aphid ipmPIPE at http://sba.ipmpipe.org for a snapshot of soybean aphid activity and Extension specialist commentary in WI and surrounding states. The current map, July 24^th shows most of WI with soybean aphid densities at zero or 1-5 aphids per plant. Over the last week, West central Wisconsin (UW Extension Buffalo County, Agriculture Agent Carl Duley) reported one field average at 84 aphids/plant. East Central Wisconsin (UW Extension Winnebago County, Agriculture Agent) reported one field at 40 aphids/plant, as did WI DATCP for one field in Columbia County (40 aphids/plant).

Additional Soybean Aphid Reports

West Central Wisconsin, July 22^nd: Reports to field crops Extension program and data from the WI DATCP pest survey indicate that Western WI counties of Dunn, Pepin, Pierce, Buffalo, and St. Croix have the highest aphid activity, although not yet at economic threshold over the area. I received a call from Gregg Kerr, CCA Kerr Agronomics, reporting a few fields from the West Central WI area nearing Economic Threshold and a couple of fields treated.

Dodge County, July 24^th : From Dodge County, UW-Extension Crops and Soils Agent Matt Hanson is detecting soybean aphids in grower fields. Averages reported today were still only 8-10 aphid per plant. Jim Fanta, Crop Consultant (NMC2), Dodge County reported non-seed treated soybean fields averaging 30-60 aphids/plant at most. Jim also made the point that although his seed treated soybean beans (i.e., CruiserMaxx treated) have been aphid-free to date, several of his seed treated fields are now becoming infested with aphids in low numbers. No reports of Economic Threshold have been reported from Dodge County to date.

Sauk County, July 24^th: Vern Meinholz, CCA, Sauk County reported soybean aphids becoming more apparent in fields this week. The highest field average Vern reported was at 50 aphids/plant. To date, I have not received reports of Economic Threshold from Sauk County.

Eastern Dane/Western Jefferson Counties, July 24th: Tom Novak, CCA, Total Crop Management, LLC reported a few fields at Economic Threshold, averaging 250 aphids/plant throughout the field, that warrant treatment. These fields comprise about 150 acres between Deerfield and Marshall.

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