Stalk borers in corn have always challenged farmers, but management has seemed especially troublesome in recent years. In cornfields where grass or broadleaf weed control was poor the previous summer, stalk borers flourish and fieldwide stand losses are possible the following spring. Stalk borers also infest corn rows that are adjacent to grass terraces, fence lines, or grass waterways.
Stalk borers lay their eggs during late summer and early fall on leaves and stems of grasses and broadleaf weeds. Grassy areas surrounding cornfields are ideal egg-laying sites. These eggs remain on the weeds through the winter and then hatch the following spring during late April and early May.
Stalk borer-damaged corn adjacent to grassy border.
Fire can be a successful management tool to kill stalk borers. Burning grass and weeds where eggs are laid greatly reduces damage from larvae in adjacent corn. George Decker, an ISU entomologist during the 1920s and 1930s, reported that stalk borer populations could be reduced 82-97 percent by burning fence lines. Recent burning experiments I conducted in central Iowa resulted in yield increases up to 68 percent in corn adjacent to burned grass terraces.
Burning grass to kill stalk borer eggs.
Burning grassy areas to kill stalk borer eggs should be done in early March in southern Iowa to very early April in northern Iowa, for several reasons. First, burning grass during early spring exposes the soil to erosion for the shortest amount of time before the grass greens up. Second, burning before the grass regrows, or right as it first emerges, does not hinder regrowth. However, don't burn after the grass has more than an inch of regrowth; southern Iowa may be past the point where burning would be desirable this spring. Third, wildlife habitat is less likely to be impacted; birds are not nesting in grassy areas during March. As a word of caution: dry cornstalks also burn so disking a firebreak around the grass before burning would be advisable.
Successful reduction of stalk borers can be a difficult task. It is best attained by using two management tactics: 1) burning grassy border areas around the cornfield, and 2) eradicating grassy weeds to prevent egg-laying in the field.
For more information, see this publication: Stalk Borer Ecology and Pest Management Options in Corn and Soybeans, IPM-41.
This article originally appeared on pages 21-22 of the IC-478 (3) -- April 7, 1997 issue.