Spring and Winter Canola: Flea Beetle

Excerpt from Agronomy Guide for Field Crops (Chapter 8)

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 Spring and Winter Canola: Flea Beetle

Description

There are two species of flea beetles that attack canola. The striped flea beetle is approximately 1.5 mm long and has two cream-coloured strips along its back. The crucifer flea beetle is bluish-black, 1.5 mm long and does not have stripes. Flea beetles jump when disturbed, hence their common name. The larvae are white, approximately 3 mm in length and have brownish heads.

Plate 139. Striped (left) and crucifer flea beetle adults. Flea beetle injury can be severe during first three weeks after emergence.

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Life History

The adult beetle overwinters in sheltered areas such as woodlots under leaf litter. In early May, adults emerge and begin feeding on newly emerged canola seedlings. Hot, sunny weather promotes feeding damage. Eggs are laid on or in the soil between May and late June. Young larvae hatch and feed on the roots of the developing crop. Larval feeding occurs for approximately 1 month from June to late July. The larvae then pupate, and adults emerge in early August and feed on canola crops until late October. The adults then locate overwintering sites. There is one generation per year.

Damage

Both the adults and larvae feed on canola, however, it is the adult stage that is considered to cause damage. Damage is most severe during the initial 3 weeks following germination. Spring adults feed on the leaves of young seedling causing a shothole appearance. Leaves and plants eventually wilt and die. Stands become thinned, and plants may become stunted. High infestations can cause up to 50% yield reduction. Once the crop reaches the three- to four-leaf stage, the crop can withstand the damage. Fall adult feeding is usually not a concern except for in winter canola. Warm, dry weather promotes feeding.

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Scouting Technique

Scout newly emerged canola fields every 2 days, especially along border rows, for the migration of overwintering adults from the fencerows and woodlots. Assess 10 plants in five locations across the field for feeding damage. Determine the average percentage of defoliation occurring. Monitor fields closely for pinhole feeding damage until the plants are past the four-leaf stage.

Action Threshold

Canola seedlings can withstand up to 25% defoliation in the cotyledon stage under good growing conditions without a significant reduction in yield. Seed treatments containing an insecticide are necessary at planting time to control flea beetles because of the difficulty in predicting their populations.

Management Strategies

Insecticide control methods should be directed against the beetle during the early stages of seedling growth. Seed treatments are available, which can be followed by foliar-applied insecticides, should beetles attack the crop after the effect of the seed treatment is gone. Seed treatment insecticides differ in the length of control of flea beetles, so some products should be used in combination with a granular insecticide, which provides longer protection. A foliar application of insecticide may be required for flea beetle control if plant growth is slow and flea beetle populations high. If damage is isolated along border edges, spot treatments can be applied. Refer to OMAFRA Publication 812, Field Crop Protection Guide, for insecticide recommendations. Canola is a valuable foraging crop for honeybees. Avoid applying insecticides during bloom. Removing cruciferous weeds such as mustards along field borders will remove alternative food sources. (Order OMAFRA Publication 812)

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Updates on Spring and Winter Canola: Flea Beetle

• Field Crop Protection Guide - Publication 812
  • Canola and Mustard: Flea Beetle

Related Links

• Canola
• Insects

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