Crucifer Flea Beetle

Causal organism: Phyllotreta cruciferae

Crops Affected: Cole crops (cabbage, broccoli, Brussels sprouts, cauliflower, kale, kohlrabi, radish, rutabaga, turnips), cruciferous crops (canola, mustard) and cruciferous weeds.

Life Cycle:

• Typically 1 generation per year
• Adults are small (2-3 mm) beetles with black/brown bodies
  • Adults overwinter in leaf litter, adjacent rough areas (headlands, field margins, fencerows, shelterbelts) or occasionally in soil
  • Adults emerge in spring when conditions are warm for extended periods
  • Adults feed on weeds and volunteer plants until cruciferous plants emerge
  • Adults lay eggs in the soil at the base of host plants, either on or near the roots – usually over a period of six weeks (end May to early July)
• Larvae feed on the roots of host plants, then pupate in the soil, to emerge as adults late in the season to feed briefly before seeking overwintering sites in September/October
• Adult activity is increased in hot, windy weather in spring and fall and feeding is increased in warm, sunny and dry conditions
  • Adults tend to prefer feeding in sunny, exposed sites, rather than in shade

Symptoms:

• Feeding by overwintered adults can produce characteristic small, round, “shot holes” in cotyledons and small leaves
  • Extensive feeding can kill young, tender seedlings
  • Some post-emergent seedling losses may occur if feeding at below ground stems girdles the stem
• Reduced plant vigour
• Delayed and uneven maturity
• Stand reduction
• Larval feeding can reduce marketability of root crops (e.g. radish, rutabaga, turnip), although feeding is often masked by other pests (e.g. cabbage maggot)

Monitoring:

• Adults are visible in sunny, exposed sights
• Using adult counts to establish economic thresholds can be difficult due to the tendency of adults to jump when disturbed
  • 75 adults per plant can lead to extensive damage in cabbage
• Look for shot hole damage on cotyledons and transplants
• Warm, dry weather can worsen damage and accelerate the rate of generational development
• Following cutting of adjacent host crops (e.g. canola), large populations of adults can arrive in crops, doing extensive damage to host crops

Management:

• Delaying seeding can reduce damage
• Increased seeding rates can compensate for feeding damage and losses
• Control cruciferous weeds and volunteer host plants
• Overhead irrigation can reduce populations of feeding adults in hot, dry weather
• Covers (e.g. Reemay) over rows or plants can reduce feeding and accelerate maturity
• There are some differences between cultivars/varieties of some vegetable host crops – e.g. waxier leaved crops tend to be less damaged that other less waxy leaved crops
• Natural predators and parasites are generally ineffective in keeping flea beetle populations down
• Registered chemical controls can be applied to control adults when first signs of shot holing appear
  • Foliar applications can be used for protection against later populations
  • Apply controls early or late in the day to slow evaporation