Flea Beetle is a minor pest that affects kale, broccoli and cabbage.
What does it look like?
Small beetles, 2 to 3mm long, black or metallic green or blue, some with a yellow stripe on each wing case. The giveaway is how they move: enlarged hind legs let them leap off the leaf when disturbed, which is usually the first sign it's flea beetle rather than another leaf-eater.
Is this pest active now?
Most active in spring and summer. OverwinteredKeeping a plant alive and intact through the cold months, whether left outdoors, moved under cover, or stored dormant. Full definition → adults emerge in mid-spring to feed on seedlings, which is the risky stage, and a later wave can arrive from nearby oilseed rape. Rain keeps the beetles off the plants, as they prefer drier conditions.
🌱 Plants at risk
Symptoms
Rounded holes scalloped out of the upper leaf surface, and damaged areas may dry and turn pale brown. Seedlings are particularly susceptible. They are the main crops affected: cabbage, broccoli, sprouts, turnip, radish and salad rocket among them, plus nasturtium.
Life cycle
Adults overwinter in leaf litter and emerge in mid-spring to feed on seedlings, exactly the stage when crops are vulnerable. Whitish-brown larvae live in the soil feeding on roots, rarely a significant problem in a home garden, before pupating in the soil in midsummer. A significant migration of adult beetles into gardens can follow later, from brassicaThe cabbage family: cabbage, kale, broccoli, cauliflower, Brussels sprouts, kohlrabi, swede, turnip and more, sharing the same pests, diseases and rotation rules. Full definition → crops nearby, oilseed rape fields especially.
Controls: what works
Tolerate the damage on established plants
Populations can be tolerated, especially on larger brassicas where the outer leaves are discarded, since the beetles usually have a limited effect on the parts you eat.
Insect-proof mesh: fine (0.8mm) or ultrafine (0.3-0.6mm)
Growing susceptible crops under insect-proof mesh may keep the beetles out. Fine mesh (0.8mm) is good for very small insects such as flea beetles, and ultrafine mesh (0.3 to 0.6mm) gives good protection against flea beetles and other very small invertebrates. Standard mesh (1.3 to 1.4mm) is unreliable against them. Bury the edges under at least 5cm of soil, and leave slack, because stretching mesh over hoops can widen the gaps.
Encourage wildlife — birds, frogs and predatory ground beetles
Encourage birds, frogs and predatory ground beetles as natural enemies of the beetles.
Natural predators of flea beetle
These 3 creatures eat flea beetle, and each has a page on how to get more of them in your garden: what to plant, or what to order and when.
Scottish grower notes
Flea beetles are most active in warm, dry, still weather and are knocked back by rain, so Scotland's cool, wet springs give emerging seedlings some natural protection. The risk window is a dry, warm spell while brassica and salad seedlings are still small; cover those with fleeceA lightweight, breathable fabric laid or draped over plants to trap a little warmth and keep off frost, wind and some flying pests. Full definition → or fine mesh until they are growing strongly.
Farm Advisory Service (FAS) Scotland crop-health guidance (2020); the biology is general, but the wet-climate framing is directly relevant to Scotland.
Myths about flea beetle
“Putting out yellow sticky traps around brassicas will control a flea beetle infestation”
Sticky traps catch flea beetles in real numbers, but catching beetles is not the same as protecting the crop. An Ohio study using traps on working urban farms removed thousands of beetles at one site over a season and the crop damage there was still high; damage only tracked trap catch at the other site, where both were low to begin with. Extension guidance is consistent on the reason: traps sample how many beetles are around, they don't intercept enough of the population reaching the plants to function as control.
What to do: Use sticky traps to tell you when beetles have arrived and whether numbers are rising, then act with mesh covers or timing changes; don't rely on the traps themselves to bring numbers down.
2 sources
- Washington State University Extension: Organic Management of Flea BeetlesSticky traps are most effective as part of scouting programs to monitor and detect flea beetle populations, not as a control method.
- Journal of NACAA: Using Sticky Traps to Control Flea Beetles on Two Ohio Urban FarmsSticky traps removed thousands of flea beetles from one farm over the season, yet crop damage at that site remained high.
“Flea beetle is one species, so a single treatment or timing works everywhere”
"Flea beetle" is a common name covering many distinct beetles, not one insect. Several species from two genera, Phyllotreta and Psylliodes, are responsible for the brassica damage gardeners see, out of more than a hundred flea beetle species recorded in Britain overall. That matters for treatment because species vary in which crops they favour and when they're active, so advice written for one region's dominant species won't map exactly onto another's.
What to do: Treat flea beetle control as a response to the damage pattern and timing you see in your own garden rather than assuming a single fixed life cycle applies everywhere.
1 source
- RHS: Flea beetles on brassicas and allied plantsSeveral Phyllotreta and Psylliodes species can be responsible, out of more than 100 species of flea beetle recorded in Britain.
“Flea beetle only threatens seedlings; once brassicas are established they're safe from it”
Seedlings are consistently named as the vulnerable stage, and RHS's tolerance advice for larger plants rests specifically on the damage landing on outer leaves that get discarded anyway, not on mature plants being immune. A US extension source goes further, older plants are described as usually able to withstand flea beetle feeding, but a heavy infestation can still cause stress, stunting, or worse in plants past the seedling stage. "Safe" overstates what any source claims.
What to do: Prioritise protection, mesh covers or raising plants past the seedling stage indoors, during the vulnerable early weeks, but keep watching larger plants under heavy beetle pressure rather than assuming they're untouchable.
3 sources
- RHS: Flea beetles on brassicas and allied plantsSeedling plants are particularly susceptible; the growth of older plants is only checked if populations are large, and populations can be tolerated on larger brassicas where outer leaves are discarded.
- University of Wisconsin-Madison Extension: Flea BeetlesRecently emerged plants are most vulnerable and can be killed by heavy infestation; older plants are often able to withstand flea beetle damage.
- Washington State University Extension: Organic Management of Flea BeetlesSevere damage can kill seedlings and young transplants, and in older plants can lead to crop stress, reduced growth, stunting, and eventual death.
“Watering brassicas at midday deters flea beetle and cuts down feeding damage”
One US university extension source says water can help deter adult flea beetles and that watering at midday may reduce their feeding, but as guidance rather than a trial result, with no figures on how much damage is saved. It doesn't appear in other flea beetle advice, which suggests it simply hasn't been tested rather than been disproven.
Our read The hedged wording, 'can help' and 'may reduce', in the one source that raises it at all is doing a lot of work; that's a fairly thin evidence base for a claim gardeners often repeat as settled fact.
What to do: Keep watering brassica beds on a normal schedule for plant health, but don't count on midday watering as your main flea beetle defence; put the effort into mesh covers and sowing timing instead.
In Scotland: Rain keeps flea beetles off plants, as they prefer drier conditions (FAS), so the effect of extra watering in a wet Scottish spring is likely to be small. No source tests it.
1 source
- University of Wisconsin-Madison Extension: Flea BeetlesWater can help deter adult flea beetles, and watering at midday may reduce their feeding.
“Covering brassica seedlings with fine insect mesh keeps flea beetle off”
Fine mesh excludes flea beetle, but the standard mesh sold for carrot fly and cabbage white is too coarse; flea beetle can leap or crawl through gaps that stop bigger insects. Both a UK and a US source point to the same failure mode: the cover has to go on before the beetles arrive and be sealed at the edges, because any beetle already inside, or any gap left along the soil, keeps it feeding under cover without birds or weather to check it.
Our read The two sources agree on the principle and diverge only on emphasis: the UK source frames it as a positive exclusion method, the US one as a warning about what happens when the seal fails.
What to do: Fit fine (0.8mm) or ultrafine (0.3 to 0.6mm) mesh over seedbeds before sowing or transplanting, and peg or bury the edges so beetles can't walk in underneath.
2 sources
- RHS: Flea beetles on brassicas and allied plantsGrowing susceptible crops under insect-proof mesh may keep the beetles out.
- Washington State University Extension: Organic Management of Flea BeetlesRow cover installed before flea beetles arrive and sealed on all sides excludes them, but if beetles get underneath they feed without interruption from predators or weather.
Frequently asked questions
What should I do first if I find flea beetle in my garden?
The first thing to try: Tolerate the damage on established plants. Then: Insect-proof mesh.
Will flea beetle kill my plants?
Seedlings can be badly damaged. Larger brassicas usually tolerate the holes, which land on outer leaves that get discarded.
When should I watch for flea beetle?
Most active in spring and summer. Overwintered adults emerge in mid-spring to feed on seedlings, which is the risky stage, and a later wave can arrive from nearby oilseed rape. Rain keeps the beetles off the plants, as they prefer drier conditions.
Should I just leave flea beetle alone?
On established plants, yes: populations can be tolerated, and birds, frogs and predatory ground beetles eat them. Protect seedlings with fine mesh.
Sources
Show the 3 sources
- RHS1: tolerance advice and its reasoning, identification, life cycle, seedling susceptibility, small rounded holes and pale brown drying, mesh, birds/frogs/ground beetles
- RHS1: ultrafine 0.3-0.6mm for flea beetles; standard unreliable
- FAS Scotland14: rain keeps the beetles off plants, as they prefer drier conditions; a pyrethroid is an option for emerging crops (commercial advice)