The common stalk borer is a slender, purple and white striped caterpillar that can be found tunneling inside the stems of a wide variety of plants. It is most commonly found inside the stalk of giant ragweed, but is of some importance as a pest of potatoes, tomatoes, corn and other plants. Samples and calls indicate the abundance of this pest is much greater than average this year.
The stalk borer moth lays eggs in the fall on grasses and weeds. These eggs hatch very early in the spring and the larvae begin boring into the grasses. During mid to late June the larvae grow to be too large for the grass stems and they move to larger plant stems in the vicinity. The borers may remain in the stem of one plant, or they may again become too large for the stem they are in and move to another host.
By the time stalk borer injury is noticed, it is usually too late to save an infested plant. There is no chemical control for borers inside the stem though plants can sometimes be saved by slicing open the stem and removing the borers by hand. Wilted plants should be considered as a source of additional borer problems and these should be removed and destroyed. The best suggestion is to keep weeds and tall grasses controlled and mowed around gardens and flowers, especially in the fall. This will help prevent future borer problems by eliminating sites that are attractive to the adult moths and the young borers.
This article originally appeared in the July 1, 1994 issue, p. 104.