By Scout Nelson
During July and August 2025, several corn fields in Martin and Mower Counties, Minnesota, showed unexpected leaf and stalk damage similar to European corn borer injury. Closer inspection revealed that common stalk borer (Papaipema nebris) larvae were causing the damage. Plants along field edges showed rows of holes in leaves, and stalk dissections confirmed larval boring.
Bt testing confirmed the presence of Cry1F, Cry2A, Cry3Bb, and Cry34/35 proteins. While Cry1F and Cry2A target lepidopteran pests like the stalk borer, some larvae survived, raising questions about movement of large larvae or potential Bt resistance. Damage was concentrated in the first 4-6 rows near grassy areas, consistent with the stalk borer’s migration from overwintered grass hosts. In one field, 60–70% of edge-row plants showed visible injury.
The common stalk borer completes one generation per year, with eggs laid in late summer on grasses and weeds along field margins, waterways, or fencerows. Eggs overwinter and hatch in late spring. Young larvae feed in grass stems before moving into corn, causing leaf feeding and stalk tunneling. Early feeding produces ragged leaf holes, and tunneling can destroy the growing point, creating wilted centers or “deadheart” symptoms. Young corn (V2-V5) is most vulnerable, though older plants can also experience localized yield losses.
Identification is straightforward: the larva has a cream-colored body with dark purple or brown stripes and a distinctive oblique black stripe across the orange head capsule. Mature larvae reach 1.5–2 inches in length, with a smooth, glossy body and dark pronotal shield. Proper identification allows farmers to distinguish stalk borer damage from other pests like European corn borer or corn earworm.
Early scouting along field edges and prompt management are key to minimizing damage. For detailed information, visit the VegEdge website on Common Stalk Borer.
Photo Credit: gettyimages-awakr10
Categories: Minnesota, Crops, Corn