Corn: Earworm

Excerpt from Agronomy Guide for Field Crops (Chapter 3)

Order OMAFRA Publication 811: Agronomy Guide for Field Crops

Table of Contents

1. Description
2. Life History
3. Damage
4. Scouting Technique
5. Action Threshold
6. Management Strategies
7. Updates on Corn: Earworm
8. Related Links...

Description

Corn earworm larvae vary greatly in colour from light green to yellow. The full-grown larvae are 4 cm (1 1/2 in.) long with prominent stripes running the length of their bodies (see Plate 20).

Plate 20. Corn earworm larva on corn ear. Larval feeding is usually concentrated at the tip of the ear.

The size and the presence of the stripes differentiate earworms from European corn borer, while their tan head colour differentiates them from fall armyworm.

Adult moths are buff or tan coloured. The forewing has a central brown dot visible from the underside of the wing, and the hind wings are pale in colour with a darker brown border.

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Life History

Corn earworm, also known as cotton bollworm - a pest on cotton, does not overwinter in Ontario but migrates as adult moths from the southern states. Usually they arrive in Ontario in August but they may come as early as late June. The moths will then lay their eggs individually on fresh silks. The eggs hatch, and the larva feed on the silks and kernels at the ear tip. Larvae will pupate but die soon after frost.

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Damage

Larvae may feed on leaves and tassels but mainly are found feeding on silks and developing kernels. Larvae damage tassels, causing poor pollination, and consume silks, affecting ear development. Fields at risk are those planted late that will be freshly silking during peak population time.

Unlike European corn borer and fall armyworms, corn earworm does not leave entry holes into the ear husk but instead concentrates its feeding at the top third of the ear tip, leaving a messy ear tip.

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Scouting Technique

Locate five sets of 10 plants per field and open the ear and inspect for feeding damage or larval presence, including the presence of ear moulds carried in by the pest. Determine the percentage of ears infested. Corn earworm is cannibalistic and, therefore, there is usually not more than one larva per ear of corn.

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Action Threshold

This pest is usually only an economic pest in sweet corn but can affect late-planted seed corn fields that are silking at time of egg laying.

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Management Strategies

Earlier-planted corn may have a chance to escape the peak infestations of corn earworm if they silk early enough. Insecticides have generally not provided economic control of corn earworm in field corn. There may be some value in treating seed corn to maintain kernel quality. Several natural enemies exist in the field, including trichogramma wasps, ladybird beetles, lacewings and parasitic flies, which help to keep pest populations in check.

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Updates on Corn: Earworm

• Field Crop Protection Guide - Publication 812
  • Corn: Corn Earworm (CEW)

Related links...

• Insects
• Corn

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