Brussels sprouts: holes eaten in leaves

What it is likely to be on brussels sprouts

1. Cabbage white caterpillars

   Candidate 1very common on this plant

   ·source

   Sourced guidancehigh confidence

   • Royal Horticultural Society: Cabbage caterpillars

   Checked 2026-08-13

   The caterpillars of the large and small white butterflies, which can strip a brassica to its midribs in a fortnight. They are conspicuous, easy to find, and almost entirely preventable by keeping the butterflies off the plants.

   Points towards it

   • · the caterpillars and their green-black droppings are both on the plant
   • · the butterflies have to reach the plant to lay
   • · large white caterpillars work outward from the heart across every leaf

   Argues against it

   • · slime points at slugs instead
   • · the butterflies do not lay on indoor plants — this rules it out entirely.

   Check this next

   Turn the leaves over and look for droppings before you look for the caterpillar. Cabbage caterpillars leave heaps of dark green frass in the leaf axils and the heart of the plant, which nothing else that eats a brassica does — and the holes are large and ragged, often reducing a leaf to its veins, rather than the neat round pits of flea beetle.

   What to do now

   Pick the caterpillars off by hand and squash the yellow egg clusters on the leaf undersides — on a domestic scale this is genuinely effective and takes a few minutes a week through late summer. Cover the crop with fine insect mesh before the butterflies are flying rather than after, because once eggs are laid under the mesh it protects them instead.

   ·source

   Sourced guidancehigh confidence

   • Royal Horticultural Society: Cabbage caterpillars — control

   Checked 2026-08-13

2. Flea beetle

   Candidate 2very common on this plant

   ·source

   Sourced guidancehigh confidence

   • Royal Horticultural Society: Flea beetle

   Checked 2026-08-13

   Tiny dark beetles that jump when disturbed and pit young brassica leaves with small round holes, giving a shot-holed appearance. Seedlings can be checked badly; established plants shrug it off, so the timing of the attack decides whether it matters at all.

   Points towards it

   • · flea beetle damage matters on seedlings and young transplants and almost nowhere else
   • · the beetles arrive from surrounding vegetation in warm dry weather

   Argues against it

   • · flea beetles leave no trail
   • · an established plant outgrows the damage and it stops being noticeable

   Check this next

   Look at the size and the number of the holes. Flea beetle makes dozens of small round pits a couple of millimetres across, giving a shot-holed or peppered look, and the beetles themselves jump like fleas when you pass a hand over the row. It is a seedling problem — the same peppering on a mature cabbage is cosmetic and needs nothing.

   What to do now

   Keep the seedbed watered — flea beetle is a dry-weather problem and a moist, fast-growing seedling grows past it. Cover early sowings with fleece or fine mesh until the plants have four or five true leaves, after which the damage stops mattering.

   ·source

   Sourced guidancehigh confidence

   • Royal Horticultural Society: Flea beetle — control

   Checked 2026-08-13

3. Bird damage

   Candidate 3very common on this plant

   ·source

   Sourced guidancehigh confidence

   • Royal Horticultural Society: Pigeon damage

   Checked 2026-08-13

   Soft fruit stripped as it ripens, and fruit buds removed from currants and gooseberries over winter. On cherries and blueberries in particular, an unprotected crop in a British garden is a bird crop, and the honest answer is netting or nothing.

   Points towards it

   • · pigeons take standing brassicas through the winter when other food is scarce
   • · a flock works across a whole plant and a whole row rather than a patch
   • · the birds are gone by the time the damage is noticed and leave no insect behind

   Argues against it

   • · an insect or a slime trail points somewhere else entirely

   Check this next

   Look at what is left of the leaf and at the calendar. Pigeons strip the soft tissue and leave the mid-ribs and main veins standing like a skeleton, over a whole plant, in the winter months when no caterpillar is flying and slugs are barely moving. Nothing else reduces a kale plant to bare ribs between November and March.

   What to do now

   Net the crop properly on a frame so the netting is held clear of the foliage — pigeons feed through netting laid straight on the plants, and birds can become tangled in loose netting. Winter brassicas usually recover and re-leaf in spring if the growing point survived, so damaged plants are worth keeping.

   ·source

   Sourced guidancehigh confidence

   • Royal Horticultural Society: Protecting crops from birds

   Checked 2026-08-13

Narrow it down

This page lists everything at once, which is the right shape for reading and the wrong shape for deciding. The interactive tool asks one question at a time, starting with whichever would separate these causes fastest, and stops as soon as further answers would not help.

Opens with the plant and the symptom already set. Nothing you answer is stored or sent anywhere — the answers live in the address bar and nowhere else.

What this does not cover

These are the causes GrowingHQ holds rules for on brussels sprouts — not every cause there is. Where several problems look alike, the honest answer is often that they cannot be told apart by eye, and a page that named one would be guessing. If none of the above fits, the general holes eaten in leaves page lists causes across all plants, and the Brussels sprouts profile lists the problems it is prone to.