Flea beetle
Phyllotreta & Altica spp.
Tiny jumping beetles that pepper seedling leaves with shot-holes, worst on brassicas and rocket in dry spells. Keep seedlings growing fast with steady water and cover with fine insect mesh.
How to know it
Glossy beetles 2–3 mm long, black or metallic blue-green, some with a yellow stripe down each wing case. They spring away like fleas at the slightest disturbance, which is usually the first thing you notice about them.
What you'll see
- Dozens of small round shot-holes peppering seedling leaves, especially rocket, mustard and turnip.
- Leaves pitted and pale where the beetle has grazed the surface without going right through.
- Seedlings checked, stunted or killed outright in a dry spell.
- A shower of tiny beetles jumping away as you lean over the row.
- Damage concentrated on the youngest leaves and on plants at the sunny end of the bed.
Where it comes from
Adults overwinter in leaf litter, hedge bottoms and rough grass, emerging in April to feed on the first brassica seedlings they find. Eggs are laid in the soil and the larvae feed harmlessly on roots; the new generation of adults appears from midsummer and feeds again before finding somewhere to winter.
Hot, dry, sunny spring weather with slow-growing seedlings is the perfect storm. Damage on established plants is cosmetic — it is only the seedling stage that is genuinely at risk.
Dealing with it
- Water generously and feed: a seedling growing fast outruns the damage, and this is the single most effective response.
- Cover the row with fine insect mesh from the day of sowing.
- Sow a fortnight later, or start in modules and plant out at a size that shrugs the beetles off.
- Run a board smeared with grease along the row and brush the foliage — the beetles jump up and stick.
- Keep the ground damp with light frequent watering in the first fortnight; flea beetles dislike humidity at soil level.
Keeping it out
- Sow brassicas and salad leaves in modules and transplant, rather than direct-sowing into an April bed.
- Rotate brassicas away from ground that carried them last year.
- Clear leaf litter and cut rough grass near vegetable beds in late winter.
- Grow a sacrificial row of rocket or mustard as a trap crop at the sunny end.
- Mulch to keep soil moisture even through spring dry spells.
What it goes for
Rocket, mustard, turnip, radish, swede and all young brassicas; also potatoes, aubergines and stocks.
- Arugula
- Asian Greens
- Bok choy
- Broccoli
- Broccolini
- Brussels sprout
- Cabbage
- Cauliflower
- Collards
- Eggplant
- Garden Cress
- Gaura
- Horseradish
- Kai Lan
- Kale
- Kohlrabi
- Komatsuna
- Mizuna
- Mustard greens
- Napa cabbage
- Ornamental Kale
- Radish
- Rat-tail radish
- Rock cress
and 11 more in the catalog
Who hunts it for you
- Big-eyed bugGeocoris spp. A stubby 3 mm bug with enormous wrap-around eyes, working the soil surface and the low foliage for aphids, mites, thrips and insect eggs. It is the main natural check on chinch bugs in a lawn and it is killed outright by insecticide. Grow to recruit it: Calendula,Clover,Cosmos,Goldenrod,Sweet alyssum
- Damsel bugNabidae A slender, mantis-armed bug that grabs aphids, small caterpillars, and thrips in low crops and meadowy edges. Leave a strip of unmown grasses and flowers for it to overwinter in. Grow to recruit it: Fennel,Sweet alyssum,Yarrow
- SpidersAraneae Webs, ambushes, and night patrols make spiders the garden’s steadiest generalist predators, taking whatever flies or crawls past. Mulch, ground cover, and undisturbed corners keep the population dense. Grow to recruit it: Lavender,Thyme
See also
The Cottage Garden Companion — the gardener's bestiary at cottagegardencompanion.com