Common Stalk Borer

Encyclopedia Article

Description of common stalk borers

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, corn, and other plants.  

Common stalk borer larva. Photo credit Adam Varenhorst
Common stalk borer larva. 
Photo credit Adam Varenhorst

Life cycle common stalk borers

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.

Damage caused by common stalk borers

By the time stalk borer injury is noticed, it is usually too late to save an infested plant. 

Management of common stalk borers

Common stalk borer adult.  Photo credit Adam Sisson
Common stalk borer adult. 
Photo credit Adam Sisson

We do not have an effective control for borers that are inside of the stem.  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. Insecticide sprays or dusts used in the garden are not effective against this pest.  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.

Do you live in Iowa and have an insect you would like identified?

The Iowa State University Plant & Insect Diagnostic Clinic will identify your insect, provide information on what it eats, life cycle, and if it is a pest the best ways to manage them.  Please see our website for current forms, fees, and instructions on preserving and mailing insects.   

Contact information for each states diagnostic laboratory for U.S. residents.  If you live outside of Iowa please do not submit a sample without contacting the Plant & Insect Diagnostic Clinic.