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Alfalfa Blotch Leafminer Found in Several Illinois Counties

June 29, 2001
Although the soybean aphid has captured most of the attention among invasive species of crops during the past couple of years, another invasive species seems to have gained a foothold in Illinois. The alfalfa blotch leafminer, Agromyza frontella (first discussed this year in issue no. 7 [May 11, 2001] of the Bulletin), invaded Minnesota from Canada in 1994. After becoming established in Minnesota, it spread throughout Wisconsin and was found in a couple of counties (Lake and McHenry) in Illinois by 1997.

Renewed survey efforts this year have revealed that the alfalfa blotch leafminer has spread considerably in Illinois. Jon Lundgren, a Ph.D. candidate in the Department of Entomology, coordinated a survey in which I, David Feltes (IPM educator at the Quad Cities Extension Center), and Jim Morrison (crop systems educator at the Rockford Extension Center) participated during the last week in April and the first couple of weeks in May. Jon has examined many samples and has confirmed the presence of the alfalfa blotch leafminer in the following 14 counties: Boone, DeKalb, Grundy, Iroquois, Kane, Kendall, Lake, Lee, McHenry, Ogle, Stephenson, Vermilion, Will, and Winnebago. Data from Carroll, Champaign, Ford, JoDaviess, and LaSalle counties have not been tabulated.

This insect has not been reported to cause much, if any, economic damage to alfalfa in the Midwest. However, its presence is worth noting. The first generation occurs at about the same time as alfalfa weevils are active, so scouts may find the characteristic blotch mines in the leaves as they monitor alfalfa fields. Probably our greatest concern is that insecticide applications to control alfalfa weevils may kill parasitoids that effectively suppress populations of alfalfa blotch leafminers. If that happens, alfalfa blotch leafminers could become problematic in some fields.

We plan to conduct a survey in mid- to late July to search for the second generation of alfalfa blotch leafminers, including a wider search into other counties. We'll keep you posted regarding any developments with this pest.--Kevin Steffey

Author: Kevin Steffey

The Pest Management and Crop Development Bulletin
Executive Editor: Kevin Steffey, Extension Entomologist

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