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Pest Alert: Soybean Aphid on Snap Beans in Minnesota

Pest Alert: Soybean Aphid on Snap Beans in Minnesota

Bill Hutchison, Dept. of Entomology, University of Minnesota, St. Paul

During the past week, Soybean Aphid (SA) populations have rapidly increased on Snap Beans at the Rosemount Agric. Research Station (UMORE Park; Dakota Co.), southeast of the Twin Cities. Infestations were very high in Wisconsin snap bean in 2001, with fewer, yet significant outbreaks also recorded in 2002. This is the first year we have observed high numbers on snap bean in Minnesota. Many beans should be in the pod filling stages now, and should soon be sprayed for European corn borer and/or Corn Earworm. However, MN growers should also check for aphids. The primary concern is the transmission of several viruses, including: Alfalfa mosaic, Cucumber mosaic. Soybean aphid can infect plants with virus, within minutes (possibly seconds) of feeding. Snap beans are not likely a preferred host, but their initial feeding/probing is adequate to transmit virus. Previous infections to the pods in Wisconsin resulted in bean discoloration and some total field losses.

At Rosemount, we have over 100 aphids per single leaflet (winged adults, apterous adults, and/or nymphs). We have not yet attempted full plant counts. The most heavily infested fields, are late-planted (June 15 and 30th), and those still in the 2nd trifoliate stage. These infestations are probably from adults that recently moved out of nearby soybean fields (we have plenty of SA infested soybean fields).

Control options/notes: For both ECB, CEW, many fields will be treated with Capture or Warrior; both materials should provided some control/suppression of SA. However, although Warrior has provided good SA control in soybeans, our results in snap beans (for both products) are thus far, inconclusive. Also, previous work with seed treatment protection (Cruiser or Gaucho) is still inconclusive regarding aphid and/or virus protection at this time (we are still collecting data).

Regarding: Dimethoate (Cygon), we have not observed very good, or lasting control of SA. Given all options currently labeled for snap bean, one of the older products (Orthene) may need to be used for aphid control, for at least one early spray (Note: 14 day pre-harvest interval), which can also provide some early ECB control.

One source of insecticide efficacy data, from MN (Ragsdale, Ostlie and Hodgson, 2001) is available at: http://www.soybeans.umn.edu/crop/insects/aphid/aphid_insecticide_trial.htm

Many of the products in the soybean insecticide trial are not labeled for snap bean, but are shown for comparison. We will provide more information as it becomes available.

Co-Editors: Bill Hutchison, Department of Entomology, University of Minnesota, hutch002@tc.umn.edu
Jeanne Ciborowski, IPM Program, Minnesota Department of Agriculture, jeanne.ciborowski@state.mn.us
Production Editor: Suzanne Wold, Research Fellow, Department of Entomology, University of Minnesota, woldx018@tc.umn.edu

Last Revised August 1, 2003.
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