Flea Beetle, Brassica
The crucifer flea beetle is uniformly black and shiny, about 2 mm in length, while the striped flea beetle has two yellow stripes on its back. These flea beetles only feed on brassica crops; those found on corn or solanaceous crops are different species.
Adults spend the winter outside the field, in shrubby or woody borders, and move into fields in May and begin feeding and mating. Eggs are laid in soil near the plant. Larvae feed on root hairs and pupate underground. New adults emerge in late July or early August and feed throughout August. Spring crops are damaged by over-wintered adults, while fall crops are damaged by summer adults. Feeding declines in September.
Adults feed on leaves and stems, leaving small round holes. Heavy feeding can kill seedlings, and moderate damage can delay maturity, reduce yield, or make crops unmarketable. Crops with more waxy leaves (cabbage, broccoli,kale) are less attractive and feeding is more restricted to leaf margins, especially as crop matures. Crops with glossy leaves (bok choy, Nappa cabbage, mustard) are highly attractive, and the whole leaf is damaged. These crops are susceptible from planting until harvest.
Monitoring & Thresholds:
Because brassica crops differ greatly in susceptibility and attractiveness there is no fixed economic threshold that applies to all crops. Beetles can be difficult to count, as they hop when disturbed. Yellow sticky cards placed in the canopy or feeding damage can be used to determine beetle populations. Control if damage to cotyledons or seedlings is stunting growth, or if damage to greens will reduce marketability.
Cultural Controls & Prevention:
- Rotate spring crops as far as possible from last season's fall brassica crops.
- Separate early and late-season brassica crops.
- Avoid early brassicas (beforeJuly) to break the reproductive cycle. (This may not be economically feasible for many growers.)
- Cover crops with spun-bonded row covers. Row cover provides excellent protection if well secured with soil or bags around all edges immediately after seeding or transplanting. Remove and replace the same day for cultivation, as needed.
- Provide adequate water and nutrients for crop growth; avoid soil compaction.
- Incorporate and till crops immediately after harvest to kill larvae feeding on roots.
For current information on production methods (including varieties, spacing, seeding, and fertility), weed, disease, and insect management, please visit the New England Vegetable Management Guide website.