University of Maryland Extension

Corn Earworm - Vegetables

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Worms in Corn

Corn earworm

Appearance 

  • Eggs: Pale green discs that turn yellowish, then gray, with noticeable ridges radiating from the center, laid singly on leaf hairs or corn silk.
  • Larvae: Caterpillars up to 1 3/4" of variable colors, ranging from green, brown, pink to yellow or sometimes black, with dark lengthwise stripes. Light brown/orange head and numerous microspines on the body are distinctive.
  • Pupae: Mahogany-brown case nearly 1” long, tapering to a short spine at tip of abdomen.
  • Adults: Moths with wingspans of 1 ¼” to 1 ¾”, having buff colored forewings with a dark spot in the center, and hind wings cream colored nearest the body and darker at the tips, with a central dark spot.

corn earworm adult moth
Corn earworm moth
Photo:
 Photo: Clemson Un. USDA Coop. Ex.
Series, bugwood.org 

Life Cycle/Habits

  • Overwinter as pupae in soil throughout the southern U.S., and as far north as Maryland in mild winters. Weather fronts bring adult moths north, with arrival beginning as early as May.
  • Night-flying moths feed on nectar and prefer corn silk for egg laying.
  • First instar (developmental stage) larvae feed on the silk and in the center of young shoots and then tunnel into kernels near the ear tip.
  • In other crops, they feed on or in unripe fruits.
  • Feeding continues for about 4 weeks and then the mature larvae drop to the soil and pupate 2-4 inches underground.
  • Two to three generations per year may occur in Maryland.

Host Plants

  • Corn is preferred, tomato is secondarily favored. Also, asparagus, cabbage, cantaloupe, collards, cowpea, cucumber, eggplant, lettuce, lima bean, melon, okra, pea, pepper, potato, pumpkin, snap bean, spinach, squash, sweet potato, and watermelon, plus many more fruits, grains, and even weeds.

Signs/Symptoms

  • Larvae feed on silk initially but may chew on young corn shoots or burrow directly into the tips of developing ears.
  • Feeding on silk may disrupt pollination, leading to kernels that do not fill out.
  • Larvae foraging into the kernels may encourage fungal growth and attract sap beetles. Ear tips are ruined and often harbor worms at harvest.
  • On tomatoes, larvae may feed on stem and foliage but mainly burrow into fruit, introducing bacteria and fungus.

corn earworm damage to corn
Corn earworm damage
Photo: Clemson Un. USDA Coop. Ex. 

Series, bugwood.org

Monitoring

  • Watch for early larval damage to young corn shoots. 
  • Eggs on tomato plants may be detected on the leaves directly below the flower clusters.

Prevention/Control

  • Select sweet corn cultivars with ear tips tightly covered by husks.
  • Bacillus thuringiensis (Bt), an “organic” pesticide, can be used on early larval stages.
  • Mineral oil dropped onto corn ear tip 5-7 days after silking prevents egg laying.
  • After silk browns, rubber band ear tips to prevent larvae burrowing into kernels.
  • Trichogramma wasps, a naturally occurring native enemy, will parasitize larvae.
  • Spring and fall tilling destroys pupae.
  • Early crops suffer less infestation than late season crops.
  • Plant extra to compensate for damage and simply cut out damaged portions.

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