University of Maryland Extension

European Corn Borer - Vegetables

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Worms in corn and peppers

European corn borer damaging corn
European corn borer (Ostrinia nubilalis)
Photo credit: Galen Dively, UME

Appearance

  • Eggs: Oval, flattened, white, usually iridescent, overlapping like fish scales, in large clusters on leaf undersides. Darken somewhat with age.
  • Larvae: Up to 1" long, pale pink or brownish-gray, hairless caterpillars with brown head and side stripe and black dots on each section.
  • Pupae: Red-brown, narrowing to a point at posterior.
  • Adult: 1" moth. Females pale yellow to brown, males darker with even darker markings.

egg mass
European corn borer eggmass
Photo: G. Dively
European corn borer adult moth
European corn borer moth
Photo: Clemson Un., USDA Coop Ex.
Slide Series, Bugwood.org

European corn borer larvae
Larva
Frank Peairs, Colorado State University, Bugwood.org

Life Cycle/Habits

  • Overwinter in stalks as mature larvae.
  • In spring, pupate and emerge as moths. 
  • Egg-laying occurs in May-June and again in July-August on leaf undersides. 
  • Larvae feed on leaves and developing corn tassels.
  • As tassels emerge, larvae bore into stalk or husk at ear tip, side, or base.
  • Usually 2-3 generations a year. 

Host Plants

  • Corn.
  • Can be significant pest on pepper fruit.
  • Secondary pest on foliage or fruit of beans, celery, cowpea, potato, rhubarb, spinach, and tomato, among others.

Signs/Symptoms

  • Borers make pinhole entrances, exuding sawdust-like frass.
  • Foliage above bored stems may wilt or break.
  • Borers enter peppers near the stem and feed on seed core.
  • In young corn shoots, feeding occurs in the central whorl of leaves and silk.
  • Older larvae do the most damage, on sweet corn boring into and feeding primarily in the ear and introducing fungi.
  • Ears will have chewed tips and kernels, with tunneling along rows of kernels and into the cob.

 damaged pepper
European corn borer tunneled into a pepper
Photo: University of GA, Bugwood.org 

pinholes and frass made by borer
Damage to stem made by borer activity
 

Monitoring

  • For young corn plants, inspect leaves for eggs masses.
  • Later look carefully into the whorl for developing larvae.
  • Pinhole entrance holes will be visible on stalks and fruit or corn husks.

Prevention/Control

  • Manage corn borers by destroying stalks, the overwintering site of larvae. Cut off stalks close to soil. Till under, shred, or remove stalks from the area.
  • Bt, an "organic" microbial insecticide can be sprayed when larvae first appear.
  • You can split infested stalks below the borer holes and then destroy this pest by poking it with a piece of wire or a nail.

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