Corn: European Corn Borer

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. Overwintering
4. Emergence
5. Development
6. Damage
7. Scouting Technique
8. Economic Thresholds
9. Management Strategies
10. Updates on Corn: European Corn Borer
11. Related links...

Description

Egg masses are flat, creamy white and layered over each other, making the egg mass appear similar to fish scales. Mature larvae are creamy white to pale grey with 2 small spots per abdominal segment, approximately 2.5 cm in length and have a black head. Adults are light-brown moths approximately 2 cm long with dark wavy lines running across each forewing. Male moths are darker and smaller than females.

Plate 15. European corn borer eggmass. Each eggmass can have 15-40 eggs, which are layered like fish scales.

Plate 16. European corn borer larvae are cream to pink with black heads and two black spots per abdominal segment. Stalk rots can be carried in by the larvae.

Plate 17. Adult European corn borer moths. Female (left) is larger and lighter in colour than the male (right).

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Life History

There are two distinct strains in Ontario. South of a line from Sarnia to Simcoe, there is a bivoltine strain that can undergo multiple generations depending on the length of the season. North of this line, there is a univoltine strain that has only one generation per year, however, locations in southern Quebec also have two generations per year. There is a band of overlap for these two strains, about 50-80 km wide along this line.

Overwintering

The insect overwinters as larvae in corn stalks and other residue left on the surface from the previous growing season. As day length increases and average day temperatures exceed ^10°C, the larvae pupate. Pupae are found within larval feeding tunnels and require 2 weeks to develop before adults emerge.

Emergence

While emergence begins around the third week of May in the southernmost regions of the province, moths do not usually appear until mid-June in eastern Ontario. Once moths emerge, they fly to nearby "action sites" or vegetative habitats such as fencerows, ditches and hedgerows along fields.

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Development

Once mated, females leave the action sites to lay eggs on the host crop. Eggs are generally laid on the underside of leaves, close to the midrib. Where univoltine ECB are present, larvae develop through the season until autumn, when as fifth instars they prepare for overwintering. Where bivoltine ECB are present, first-generation larvae will pupate in mid-summer, emerge as adults and complete a second generation before entering diapause in the fall.

Damage

Early-season larvae feed on leaves, creating small pinholes and eventually migrate into the whorl of the plant and attack the enclosed tassel. Later-season larvae feed briefly on the leaves, bore into the midrib of the leaf and then migrate into the stalk of the plant and husk of the ear. Larvae may also feed directly on the developing kernels. Stalk lodging and ear droppage may occur as a result of significant infestations. This pest can carry both stalk rots and ear rots into the plant. High-risk factors include no-till fields with high residue, those with frequent corn crops in cycle, regions with a high percentage of corn (50% or greater in region) and regions where univoltine and bivoltine strains overlap.

Scouting Technique

Early-season moths are attracted to taller, early-planted corn fields while later-planted fields are more susceptible to second generation corn borer where female moths are attracted to silking and tasselling fields. Examine a minimum of five sets of 20 plants per field (100 plants per field).

For first generation scouting, look for leaf-feeding damage. Pull out and unroll the whorl of the damaged plants, looking for small larvae. Split the stalk of the plants from top to ground to locate older larvae. Record the percentage of damaged plants and number and size of larvae found.

For second generation scouting, look for egg masses on the underside of the leaves, close to the midrib of the plant. Concentrate scouting efforts to the three leaves above and below the ear of the plant. Record the percentage of plants with egg masses. Repeat scouting every 5 to 7 days until peak moth flights have subsided in your region (approximately 1 month).

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Economic Thresholds

Refer to Appendix E, European Corn Borer Economic Threshold Calculations, to calculate ECB economic thresholds.

Management Strategies

If ECB is a moderate to high risk in your region, consider planting transgenic Bt corn hybrids. Use corn hybrids that express the Bt toxin in the ear as well as the stalk to help avoid stalk and ear rot.

If using Bt corn, it is imperative that a refuge of at least 20% of non-Bt corn is planted along with the Bt corn to reduce the chance of developing resistance to Bt. This refuge can be achieved by planting strips of at least six rows wide (e.g., three planter boxes on an 8-12 row planter) or by planting blocks of non-Bt corn. In all cases, all Bt corn plants should be within 400 m of non-Bt corn. Do not mix Bt and non-Bt seed to achieve refuge. Do not apply ECB Insecticides in refuge.

Insecticides have generally not provided economic control of ECB in field corn. Using Bt transgenic corn provides much better control. Shredding debris after harvest is an effective way to destroy borers overwintering in stalks and stubble; leave as little stalk as possible. Select hybrid varieties of corn with resistance or tolerance to ECB feeding and adapted to your area. Immature stages of ECB are attacked by natural enemies, which contribute to reducing population densities. Predators such as ladybird beetles and minute pirate bugs feed on the eggs and young larvae. Parasitic wasps and predaceous mites can also help to control this pest.

For further information on ECB or Bt corn, refer to OMAFRA Publication 12, Sweet Corn Production Manual, and the Canadian Corn Pest Coalition publication, A Grower's Handbook; Controlling European Corn Borer With Bt Corn Technology, available at www.ontariocorn.org/btguide.html.
(Order OMAFRA Publication 12).

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Updates on Corn: European Corn Borer

• Field Crop Protection Guide - Publication 812
  • Corn: European Corn Borer (ECB)

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Related links...

• Insects
• Corn

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