Corn: European Chafer (White Grubs)

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 Thresholds
6. Management Strategies
7. Updates on Corn: European Chafer (White Grubs)
8. Related links...

Description

European chafer larvae are white and C-shaped with an orange-brown head and dark posterior. This pest can be distinguished from other white grubs by its Y-shaped pattern of anal bristles known as "rasters," located on the underside of the last abdominal segment of the larva. The adult is a medium-sized, light-brown, fawn-coloured, oval scarab beetle, closely resembling the native June beetle.

Plate 10. European chafer larvae are white with an orange-brown head and dark posterior. They are distinguished from other white grubs by the Y-pattern of the anal bristles (rasters).

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Life History

This pest overwinters as larvae or "grubs" in the soil below the frost line. In April to mid-May, these larvae migrate back up close to the soil surface and feed on plant roots. Larvae then pupate from mid-May to mid-June, and adult beetles emerge from the soil in early June to early July to mate. Adult chafers congregate in conspicuous mating flights and can be seen swarming at dusk. The beetles fly to tall objects along the horizon, usually trees or other landscape to mate. The adult females then locate cool, moist soil in nearby fields or lawns to lay their eggs in. Eggs hatch and newly hatched larvae begin feeding on roots in late July until the ground freezes. The grubs then migrate down below the frost line to overwinter. There is one generation per year.

Damage

Grubs feed on the fibrous roots, 3-5 cm from the soil surface. Roots are pruned, causing plants to become stunted and wilt. Intense root feeding results in poor emergence and stunted plants. Corn following soybean crops on sandier soils near areas of turf such as lawns, golf courses and pasture is at the highest risk.

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Scouting Technique

It is best to scout for chafers in the fall in standing soybean stubble. Scout for chafers on the sandier knolls of the field. Using a shovel, dig up approximately 1 ft of soil, about 3-4 in. deep, for five single soybean plants in each area sampled.

Action Thresholds

No thresholds are available at this time.

Management Strategies

See OMAFRA Publication 812, Field Crop Protection Guide, for chemical control options. Avoid planting corn if grub population is extreme, plant soybeans instead. Cultural options include disturbing the soil by tillage or disking, which brings the grubs to the surface where they are exposed to the elements and natural enemies such as birds, skunks, raccoons etc. To be effective, fall plowing must occur before the grubs migrate below the plow depth. Some natural enemies help to control this pest, including parasitic wasps (e.g., pelecinid wasp), parasitic flies, pyrgotid fly and fungus. (Order OMAFRA Publication 812)

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Updates on Corn: European Chafer (White Grubs)

• Field Crop Protection Guide - Publication 812
  • Corn: European Chafer (White Grub)

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Related links...

• Insects
• Corn

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