Plant Health Initiative

Stem Borer - Life cycle

White or yellow grub-like larvae tunnel down the petiole into the soybean stem. Photo by Phil Sloderbeck © Kansas State University

Insect-induced lodging. The plants will often be broken off smoothly at the soil line. Photo by Phil Sloderbeck, © Kansas State University

The adult soybean stem borer lays eggs from June through August in the leaf petioles at mid-canopy. The eggs hatch into white or yellow grub-like larvae which tunnel down the petioles and into the stems.

This tunneling causes the leaves to wilt and eventually fall off the plant after the larva enters the main stem.  Larvae usually will have tunneled to the base of the plant by the time the plants reach physiological maturity. Once the larva reaches the base of the plant they can girdle plants internally, often causing the entire plant to fall over (lodge) . 

The larvae overwinter below ground in the base of the root. Larvae pupate in the spring and adults emerge to begin the cycle again.

Since this is a native insect it also has several wild hosts including cucklebur, rag weed, and wild sunflower. It has also been reported as a pest of cultivated sunflower where it has been referred to as the sunflower stem girdler.