Flea beetles on cabbage family
Brassica flea beetles are one of the primary reasons spring-planted kale, cabbage, and broccoli seedlings sometimes look terrible in May -- and one of the reasons fall-planted brassicas need a management plan before they go in the ground. The striped flea beetle and crucifer flea beetle are both.
—- title: "Flea beetles on cabbage family" slug: flea-beetles-on-brassicas hub: problems category: "Disease-by-host" description: "Flea beetles create shot holes across brassica seedlings in spring and fall. Identify the striped and crucifer species, protect seedlings with row cover, and manage fall crops with delayed planting or traps." date: 2026-06-10 updated: 2026-06-10 author: "Thomas A." reading_time: 8 —-
Brassica flea beetles are one of the primary reasons spring-planted kale, cabbage, and broccoli seedlings sometimes look terrible in May — and one of the reasons fall-planted brassicas need a management plan before they go in the ground. The striped flea beetle and crucifer flea beetle are both common in the eastern US and feed almost exclusively on brassicas, meaning populations build wherever brassicas have grown previously.
I don't grow brassicas at my Long Island property, so this guide draws on Cornell Cooperative Extension, Penn State Extension, and Clemson HGIC research.
The pests
Striped flea beetle (Phyllotreta striolata)
Per Cornell Cooperative Extension, the striped flea beetle is one of the most common flea beetles on brassicas in North America. Adults are 2mm, black with two curved yellow stripes on the wing covers.
Crucifer flea beetle (Phyllotreta cruciferae)
Per Penn State Extension, the crucifer flea beetle is uniformly metallic blue-black, 2mm. It is one of the most damaging flea beetle species on brassicas in the mid-Atlantic and northeast.
Both species are host-specific to the mustard family (Brassicaceae) and do not infest tomatoes, eggplant, or other vegetable families.
Identification
The beetles
Per Penn State Extension, brassica flea beetles:
- 2mm; striped or uniformly dark
- Jump rapidly when disturbed; flying is also common
- Active on warm, sunny days; less active in cool, cloudy weather
- Found on upper leaf surfaces of young seedlings
Damage
Per Clemson HGIC:
- Numerous small, round shot holes in cotyledons and true leaves — the classic flea beetle damage pattern
- Holes are 0.5–3mm diameter; in heavy infestations the entire leaf surface may be riddled
- Young seedlings with extensive damage may not recover
Per Cornell Cooperative Extension, the damage pattern in brassicas is often more severe than in solanaceous crops because brassica seedlings are slow-growing and take longer to outgrow the vulnerable stage. Kale and arugula seedlings are particularly vulnerable; mature cabbage and broccoli plants are rarely significantly damaged.
Seasonal pattern
Per Penn State Extension:
- Spring: Adults overwinter in leaf debris and soil; emerge in April–May and immediately seek host plants; peak pressure coincides with spring brassica planting (April–June in the northeast)
- Summer: Adults estivate (summer dormancy) in cool, shaded refugia during hot weather
- Fall: Adults re-emerge in late August–September; peak pressure coincides with fall brassica planting
Both planting seasons have distinct flea beetle pressure windows. Fall crops face a second generation of fresh adults — which is often more damaging than the spring pressure because populations have had all summer to build.
Management
Row cover
Per Penn State Extension, floating row cover (0.5 oz/sq yard or heavier) applied at seeding or transplant and sealed at the edges is the most consistently effective management tool. For spring crops, leave in place until plants are 6–8 inches tall. For fall brassicas, use row cover for the first 4 weeks after transplant.
Per Cornell Cooperative Extension, ensuring the cover edges are thoroughly sealed — buried in soil or weighted with boards — is critical. Flea beetles are very small and will find any gap.
Delayed planting for fall crops
Per Cornell Cooperative Extension, planting fall brassicas in late August (in the Northeast) rather than late July delays the seedling-sensitive stage until after peak fall flea beetle populations subside. This is a scheduling strategy that avoids the worst pressure without any pesticide use.
Trap cropping with arugula
Per Penn State Extension, arugula is a highly preferred host for brassica flea beetles. Planting arugula borders around the main brassica planting concentrates beetle activity in the trap crop rows, where they can be treated with insecticide or physically removed. Research at Cornell showed arugula trap cropping reduced flea beetle damage on kale by 60–80% in some trials.
Kaolin clay
Per Clemson HGIC, kaolin clay (Surround WP) applied to foliage deters flea beetles by creating a particle film that irritates them. OMRI-listed for organic production. Apply preventively, beginning at seeding or transplant, and reapply after rain.
Insecticides
Per Penn State Extension, for spring crops where row cover is removed before harvest (some cole crops need pollinator access), insecticides provide targeted control:
- Spinosad — effective contact and stomach activity; 7-day reapplication
- Pyrethrin — organic option; short residual; 3–5 day reapplication
- Permethrin — effective synthetic pyrethroid; longer residual; observe pre-harvest intervals
Apply in cool, overcast conditions or in the early morning when beetles are less active and more likely to remain on treated foliage.
Common problems table
| Symptom | Likely cause | Action |
|---|---|---|
| Shot holes across all brassica seedlings | Crucifer or striped flea beetles | Apply row cover; apply kaolin or spinosad |
| Fall brassica seedlings heavily damaged in late August | Fall flea beetle emergence | Delay fall planting; use row cover |
| Mature cabbage/broccoli with minor shot holes | Flea beetles on established plant | No intervention needed; plants tolerate it |
| Arugula heavily attacked, kale untouched | Trap crop working | Apply insecticide to arugula; protect main crop |
Frequently Asked Questions
Why is arugula effective as a trap crop when it's in the same plant family?
Per Penn State Extension, brassica flea beetles prefer arugula to most other brassicas, probably due to its volatile compound profile. When given a choice, beetles concentrate on arugula, making it possible to focus control in one location rather than across the entire planting.
Can I plant spring brassicas and fall brassicas in the same location?
Per Cornell Cooperative Extension, rotating between beds year-to-year reduces the population of overwintering flea beetles at each site. However, because both striped and crucifer flea beetles are mobile and can fly into gardens from surrounding areas, rotation has limited effectiveness compared to physical exclusion.
Do flea beetles affect seedlings differently than direct-seeded plants?
Per Clemson HGIC, transplants with large root systems and established canopy tolerate flea beetle feeding better than direct-seeded plants at the cotyledon stage. When possible, starting transplants under row cover before field placement gives them a head start.
Does flea beetle damage affect the flavor or safety of harvested brassicas?
Per Penn State Extension, flea beetle feeding scars are cosmetic and do not affect the safety or nutritional content of harvested vegetables. Kale and cabbage with minor shot-hole scars are completely safe to eat.
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Recommended gear: Best Floating Row Covers for Pest Exclusion (2026) — our buyer's guide covering picks for every budget, ranked by Extension publication consensus and personal use.
Sources
- Penn State Extension — Flea Beetles in Vegetable Gardens
- Cornell Cooperative Extension — Brassica Pest Management
- Clemson HGIC — Flea Beetles