Flea beetle
Phyllotreta spp.
Role in the garden
A tiny jumping beetle, a few millimetres long, that riddles leaves with small round holes; devastating on young Brassica seedlings in spring.
How to attract / manage it
Insect netting over young seedlings, soil kept cool, trap crops.
Practical guide
Where to find them
Mostly Brassicaceae (cabbage, radish, turnip, kohlrabi, rocket, watercress, mustard); related species (Epitrix, Psylliodes) also hit Solanaceae (potato, aubergine). Adults active in hot, dry weather from 10-12 °C; they jump like fleas when disturbed.
Prevention
Sow densely then thin; cover young plants with insect netting (fine mesh) from sowing; keep the soil cool and mulched (flea beetles avoid moisture); water as a fine spray; sow trap crops (sacrificial rocket, radish); avoid large bare stretches of brassicas and encourage biodiversity.
Early signs
Leaves riddled with small round holes ('shot-holing'), especially on cotyledons and young leaves; radish or rocket seedlings that stall; a cloud of tiny beetles jumping as your hand passes.
Action / control
Early in the morning (torpid insects), sweep a glue board over the foliage or vacuum the adults; step up watering and mulching. No method eradicates them entirely: prevention (netting + cool soil) comes first. Avoid insecticides, even 'organic' ones (pyrethrum), which are toxic to beneficial insects.
Sources
- FREDON Hauts-de-France, fiche technique « L'altise des crucifères (Phyllotreta spp.) »
- DRIAAF Île-de-France (ministère de l'Agriculture), ravageurs des choux
- Jardiner Autrement (programme ITAB/INRAE), fiche Radis / Altise
Favourite plants / resources
Related plant entries
Radish
A brassica with an ultra-short cycle (3-4 weeks in spring), the best row-marker for slow sowings (carrot, parsnip). Lets you occupy a space while waiting for the main crop. To be avoided before cabbage (same family, common clubroot).
Cabbage
A brassica with a long rotation: 4 to 5 years between two brassicas, 8 to 10 years after a clubroot attack (Réussir Fruits & Légumes, 2022), whose spores (Plasmodiophora brassicae) can contaminate the soil for up to 20 years (RHS). Very greedy (nitrogen, calcium, water). To be planted after a legume to benefit from the nitrogen.
Turnip
A fast-growing root brassica (5 to 8 weeks): ideal as an intercrop between two longer crops, or in succession after peas to use the fixed nitrogen.
Brussels sprouts
A late long-season brassica: occupies the soil from April to February. An excellent autumn and winter transition plant, to be earthed up for stability. Pinching out the head ('topping') in late August encourages the sprouts to swell evenly. Frost converts starch into sugars: the sweetest harvest is after the first frosts.