This article was published originally on 7/1/2009
The common stalk borer is a slender, purple and white striped caterpillar 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 tomatoes, peppers, corn and other plants.
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-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. Spraying insecticides after the caterpillars are inside the crop stem is not effective. 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 eliminate sites that are attractive to the adult moths and the young borers.
Stalk Borer: The coloration is distinctive: purple and white stripes except for a band near the middle of the body. Photo by Marlin Rice.