Corn Rootworm Damage Reports from 1st Year Corn

Eileen Cullen, Extension Entomologist, UW Entomology Department

Reports of corn rootworm larval damage on first year corn have been received over the last two weeks. Jim Stute, UW-Extension Rock County Crops/Soils Agent reported a field corn field (following soybeans) with extensive root damage (2 to 3 nodes of roots pruned) near LaPrarie, WI.  Also in Rock County, Eric Birschbach, AgSite Crop Consulting, Verona, WI reported similar damage in a first year seed corn field following soybeans near Evansville, WI. Since 2003, UW Entomology/UW-Extension and cooperating producers have documented Variant western corn rootworm (also known as “soybean variant” or “rotation resistant”) in Rock County. On July 12^th, Tim Bender, UWEX Jefferson County Crops/Soils agent received his first report in Jefferson County of first year corn following soybeans showing severe root feeding damage (2 nodes of roots entirely pruned).  The report was received from south of Rome, WI, called in by Kris Duffy, Agronomist with United Cooperative.

The Jefferson county report fits the pattern of known Variant western corn rootworm presence in southeastern Wisconsin (Rock, Walworth, Racine and Kenosha); as well as increased incidence north of this initial focal point. Matt Hanson, UW-Extension Dodge Co. Crops/Soils Agent and his cooperating producers detected 6 beetles/trap/day in one of five soybean fields trapped in 2005 along the southern tier of townships in Dodge County. This field exceeded the threshold of 5 beetles/trap/day, based on 12 Pherocon AM yellow sticky traps placed in the soybean field and monitored for 4 weeks late July through the August 2005. Matt and UW Entomology will be assessing corn root condition in all 5 of his sentinel fields this month, as well as the entire Network – following up 2005 soybean sticky trapping with 2006 first year corn root evaluations from the same field locations.

First year corn following soybean, near LaPrarie, WI 2006.  Corn rootworm larval damage. Photo courtesy of Jim Stute, UWEX Rock County

During the week of July 24^th-28^th, the UW-Extension SE Wisconsin Variant Western Corn Rootworm Trapping Network in collaboration with the WI DATCP Pest Survey, will be placing yellow sticky traps in 90 soybean fields distributed over 17 counties. The Network will be tracking western corn rootworm beetle captures on the sticky traps (12 traps per field) over a 4-5 week period covering the month of August to determine Beetles/Trap/Day. Reports from the Variant Network will be provided in Wisconsin Crop Manger articles later this summer and fall detailing results from our 2006 first year corn root sample and 2006 soybean sticky trap monitoring.  Adult western corn rootworm beetle counts from 2006 will be summarized to describe the geographical range/movement of this insect pest in WI and to alert producers to management considerations for first year corn in 2007.