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Alfalfa Blotch Leafminer Confirmed in Will County

May 11, 2001
During the past 3 years or so, we have addressed the alfalfa blotch leafminer in some issues of the Bulletin. The alfalfa blotch leafminer was first introduced into North America (Massachusetts) in 1968, but it's a relative newcomer to the Midwest. Experts believe the leafminer was introduced into Minnesota from Canada in 1994. Between 1994 and 1997, the leafminer spread throughout Minnesota and Wisconsin and was detected in two counties in Illinois--McHenry and Lake. Since that time, we have not learned much more about this introduced pest.

In 2001, Jon Lundgren, a Ph.D. candidate with Rob Wiedenmann, biological control specialist in the Center for Economic Entomology at the Illinois Natural History Survey, initiated a survey effort to see whether the alfalfa blotch leafminer still is present in Illinois and, if so, where it occurs. David Feltes, IPM educator, Quad Cities Extension Center; Jim Morrison, crop systems educator, Rockford Extension Center; and I are helping Jon with the survey effort. During the week of April 30 and continuing into the week of May 7, we started surveying all counties north of I-80 (except Cook and DuPage), including those counties through which I-80 passes: JoDaviess, Stephenson, Winnebago, Boone, McHenry, Lake, Carroll, Ogle, DeKalb, Kane, Whiteside, Lee, Rock Island, Henry, Bureau, LaSalle, Kendall, Grundy, and Will. Although we have not completed the survey, Jon has confirmed finding adult alfalfa blotch leafminers (four per 100 sweeps) and a little pinhole injury in a field in Will County. He also believes he may have collected the primary parasitoid, Dacnusa dryas, in Will County.

Jon has a lot of samples to examine, but I thought that the initial finding was worth mentioning. There's nothing to become terribly excited about, but it is noteworthy that the pest has found its way farther south into Illinois than its original occurrence. We probably will extend our survey efforts south of Will County to determine its current distribution in Illinois.

The alfalfa blotch leafminer is capable of becoming an economic problem, although the presence of natural enemies often keeps leafminer densities below economic levels. Knowing that it is present in Illinois alfalfa now, even in low numbers, will enable us to mount an educational campaign to alert producers and others about what to look for and when.

I will provide updates of our findings in future issues of the Bulletin.--Kevin Steffey

Author: Kevin Steffey

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

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