Bryan Jensen
UW Extension
Depending on your location, stalk borer movement from grassy weeds to corn has, or will soon start. Although control with foliar insecticides is effective, timing is critical. Stalk borers overwinter as eggs laid on perennial grasses such as quackgrass and wirestem muhly during late August and September. Use your fall weed surveys to locate these area and/or concentrate your scouting efforts along fencerows, ditch banks, terraces, etc. After hatch, larvae will begin feeding inside grassy weeds as well as some broadleaf weeds. Soon those larvae will leave these early hosts and migrate into the first few rows of corn.
Stalk borers damage corn by feeding within the whorl then moving down into the stalk or by entering the plant directly into the stalk above ground. Initial feeding symptoms include light scarring of leaf tissue, holes in leaves and eventually wilted whorls. Treatments are best timed during the migration to corn but prior to larvae burrowing into the corn stalk. Larvae cannot be controlled once they have burrowed into the stalk and treatment after V7 is not suggested.
Treatment thresholds have been developed by Iowa State University and available for your review in Pest Management Fast Facts, https://ipcm.webhosting.cals.wisc.edu/download/pubsPM/Pest-FastFacts.pdf Insecticide treatment options are available by navigating to Pest Management Mobile http://pmm.uwex.edu/ or UW Extension Publication A3646, Pest Management in Wisconsin Field Crops http://learningstore.uwex.edu/Pest-Management-in-Wisconsin-Field-Crops2008-P155C37.aspx
