Pest profile

Common Stalk Borer

Papaipema nebris · Lepidoptera: Noctuidae[3]

The common stalk borer is a slender, purple-and-white striped caterpillar that tunnels inside the stems of many plants; it is most common in giant ragweed but also damages tomatoes, corn and garden flowers.[1]

Common stalk borer moth, brown with small white spots on the forewings
Common stalk borer moth, brown with small white spots on the forewings. (c) Dan MacNeal, some rights reserved (CC BY) — via iNaturalist, CC BY 4.0

How to identify it

  • The caterpillar is slender with purple and white stripes and is found inside plant stems.[1]
  • The usual sign is a plant that suddenly wilts because a borer is tunneling inside the stem.[1]

Where it lives

Iowa State and South Dakota State Extension both report it; SDSU tracks its movement into corn with degree days.[1][2]

US map: public records from 32 states since 1990 (GBIF).

Biology and life cycle

Moths lay eggs in fall on grasses and weeds; the eggs hatch very early in spring, and the young caterpillars bore into grass stems.[1]

In mid to late June, caterpillars outgrow the grass stems and move to larger plants nearby, sometimes moving again to another host.[1]

SDSU uses degree days above 41°F: eggs begin hatching at about 575 degree days, 10 percent of caterpillars start moving to corn at 1,300, and half have moved by 1,400.[2]

Damage and signs

  • Caterpillars tunnel inside stems, and by the time injury is noticed it is usually too late to save the plant.[1]
  • In corn, the first sign is defoliated leaves along field edges next to weedy areas.[2]

Health risk

None to people or pets.[1]

Control

Prevention

Keep weeds and tall grass mowed around gardens and flower beds, especially in fall, so moths have no place to lay eggs.[1]

Traps and physical control

Plants can sometimes be saved by slicing the stem open and removing the borer by hand; remove and destroy wilted plants, which can harbor more borers.[1]

Pesticides

Insecticide sprays and dusts used in the garden are not effective against borers inside stems.[1]

Common questions

Why did my tomato plant suddenly wilt?
One possible cause is a common stalk borer tunneling inside the stem.[1]
Will spraying kill stalk borers?
No; garden sprays and dusts don't reach borers inside the stem.[1]
How do I prevent stalk borers?
Mow weeds and tall grass around the garden, especially in fall, since moths lay their eggs there.[1]

Sources

  1. Iowa State University Extension and Outreach (Yard and Garden), “Common Stalk Borer.” yardandgarden.extension.iastate.edu/encyclopedia/common-stalk-borer (accessed 2026-10-15)
  2. South Dakota State University Extension, “Common Stalk Borer Activity Estimate: June 5, 2024.” extension.sdstate.edu/common-stalk-borer-activity-estimate-june-5-2024 (accessed 2026-10-15)
  3. iNaturalist, “Papaipema nebris taxon page (order and family).” www.inaturalist.org/taxa/1654142 (accessed 2026-10-06)

Updated 2026-10-15. Built from sourced records. Spot an error? Tell us.