If temperatures begin to warm up, stalk borer injury could be evident in these counties during the week of May 19. Egg hatch will have begun in counties in the central one- third of the state. By examining the Figure 1, you should be able to determine the approximate stage of development of stalk borers in your area. You likely will not find the smaller larvae, but as they grow larger and begin to feed on corn seedlings, the distinguishing characteristics become evident. Later in the season when the larvae bore into the corn stalks, the purple band fades and virtually disappears.
Stalk borers tunnel into corn stems above the soil surface or climb into the whorl.
Whorl feeding by stalk borers results in tattered leaves but has no long-term impact on development or yield. However, stalk borers that tunnel into the plant cause more serious problems. After plants grow to the 8-leaf stage, corn usually tolerates feeding with no visible injury. Grassy field edges and grass waterways are attractive, relatively permanent egg-laying sites for the moths in late summer and fall. Consequently, corn next to these areas often becomes infested when the larvae outgrow their grass hosts and move into the field.