Soybean Aphid Densities are Low, But Start Scouting Now

Eileen Cullen, Extension Entomologist

Wisconsin soybeans have yet to see economic soybean aphid densities. Statewide, field averages continue to be well below the economic threshold of 250 aphids/plant. However, soybean aphids are present in fields and the time to begin scouting is now.

Growers and consultants should begin monitoring soybean fields for soybean aphid, and many have been scouting for a couple of weeks now. Regular field scouting will be important from late vegetative/beginning bloom, all the way through the R5 growth stage as seeds develop in the pods.

Check 20-30 plants per field, from 80% of the field to obtain a representative sample. Examine the entire plant, particularly new growth at the top of plants. Use the economic threshold of 250 aphids/plant (field average). Regular field visits are required to determine if soybean aphid populations are increasing. 

Soybean Aphid Scouting and Management Resources for 2009

UW Soybean Plant Health website for information on 2009 Soybean Aphid Management. Includes scouting, economic threshold and insecticide management information-

www.plantpath.wisc.edu/soyhealth/aphids/aphid_management.htm

Soybean Aphid ipmPIPE

http://sba.ipmpipe.org 

Soybean Aphid Biological Control

Provides new information on soybean aphid predators and parasitoids in Wisconsin and the North Central States

http://www.entomology.wisc.edu/sabc/

Wisconsin Pest Bulletin, WI DATCP

http://pestbulletin.wi.gov/

Soybean aphid densities are also very low in my program’s conventional and organic research plots at Arlington, WI where we are averaging less than 20 aphids per plant. In our counts, we find the occasional ant-tended plant with 100-200+ aphids, but overall plot averages are typically 10 aphids/plant or lower. However, our research plots are about 50% infested so there is a very low soybean aphid density fairly well distributed in our plots, which could lead to economic populations in the coming weeks.

Krista Hamilton, WI DATCP Pest Survey and WI Pest Bulletin http://pestbulletin.wi.gov/ reported last week’s state survey of 61 Wisconsin soybean fields in the V1-V5 growth stage. WDATCP surveys in Columbia, Dane, Green, and Rock counties found 1-18 aphids/plant on 5-60% of plants in the fields checked. In Grant, Iowa, Lafayette and Sauk counties, densities ranged from 3-163 aphids/plant on 25-70% of plants. Moderately infested soybean fields may develop economic populations within the next two weeks. In the central counties of Adams, Fond du Lac and Marquette, densities varied from 2-11 aphids per infested plant on 5-38% of plants. No aphids were detected in 61% of the fields appraised in the southern half of the state.

I am also providing soybean aphid scouting report updates for Wisconsin at the online pest tracking system, ipmPIPE – the Integrated Pest Management - Pest Information Platform for Extension and Education http://sba.ipmpipe.org . The ipmPIPE is a good place to get a quick state and regional look at soybean aphid densities and Extension commentary on soybean aphid management recommendations. The ipmPIPE data should be used as ‘sentinel’ plots to help you gauge changing soybean aphid conditions throughout Wisconsin. Always conduct local and on-farm field scouting before you decide to treat a soybean field for soybean aphid. Regional mapping data should be used for general sentinel purposes only. 

Thank you to UW Extension County Agricultural Agents and the WI DATCP Pest Survey who are all contributing weekly soybean aphid scouting information to our Wisconsin map on the ipmPIPE.