Degree day accumulations (base 41º) in southern Wisconsin indicates stalk borer eggs are hatching and migration to corn can be expected soon. Although there hasn’t been a lot of interest in their control recently, high corn/input prices may indicate a closer look this year. 

 

Stalk borers overwinter as eggs laid on many grass weed species and even some broadleaves. After spring egg hatch, larvae will feed within perennial grasses (i.e. quackgrass and wirestem muhly) but once larvae are too large for these stems they will disperse into corn. 

 

Focus scouting efforts where there was significant egg laying sites last fall and where you might have patches of perennial grasses (i.e., fence rows, grassy waterways, terraces, etc.) this spring. Usually this migration is limited to the first few rows of corn which makes spot application desirable and economical.

 

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. Symptoms of feeding include light scarring of leaf tissue, holes in leaves and eventually wilted whorls. Spot treatments are best timed when migration to corn is nearly completed and prior to larvae burrowing into the corn stalk.    An economic threshold table has been established by Iowa State University and is available in UW Extension bulletin, A3646, Pest Management in Wisconsin Field Crops:2008   http://learningstore.uwex.edu/Pest-Management-in-Wisconsin-Field-Crops2008-P155C37.aspx see page 64.   Although current market trends were not reflected in this table by the October, 2008 publication date, you should be able to extrapolate for current/expected corn prices.