Biological control of WBC promising
The western bean cutworm is a serious pest of dry edible beans and corn in Nebraska, and is now expanding its range eastward to as far as Pennsylvania and Ontario.
Typically, farmers use chemicals to control western bean cutworms in dry beans; however, down the road there may be another option. A new biological control method that was tested in the Panhandle showed promise as an alternative control measure. UNL Extension Entomologist Jeff Bradshaw said more research is needed, but a 2011 study near Scottsbluff showed that the parasitoid, Trichogramma ostrinae, preyed on western bean cutworm eggs in dry beans and corn.
Trichogramma have been used successfully in China against the Asian corn borer and in the eastern United States against the European corn borer, so Bradshaw is encouraged by the fact that they also will prey on western bean cutworm in bean and corn fields.
Trichogramma ostrinae, a tiny wasp, is a native parasitoid of the Asian corn borer. In the early 1990s it was introduced into the eastern United States for control of the European corn borer in sweet corn. The Scottsbluff study was intended to find out whether trichogramma would prey on the eggs of western bean cutworm in corn and dry beans.
Bradshaw noted that much is not known about western bean cutworms. There are no highly accurate sampling programs in dry beans, and little knowledge about what factors control the spread of the pest.
Adding biological control to the arsenal of management options has several advantages, Bradshaw said. Chemical control has economic and environmental costs and requires aerial application due to the point in the season when it would be applied — when the rows have closed and equipment can not longer be driven through. The per-acre cost of aerial application is affordable only if there are enough acres to spray in one area. Researchers and some bean growers are experimenting with more upright, less viney plants that allow direct harvest with a combine, instead of a multiple-step process of cutting, windrowing and swathing. But most bean acres still consist of viney, low-growing plant types.
Trichogramma Targets Limited
Although the trichogramma wasp comes from China, it is not expected to become an invasive species in the United States, Bradshaw said. Extensive studies from Cornell University and the U.S. Department of Agriculture’s Animal and Plant Health Inspection Service (APHIS) have shown only 13 species of Lepidoptera, such as European corn borers, diamond back moths, and now western bean cutworms, are attacked. It has also been used on the East Coast against European corn borers in sweet corn to economic benefit.