Why Do My Brussels Sprout Leaves Have Lots of Holes?

Holes in Brussels sprout leaves are one of the most common complaints from home growers. The damage can appear overnight and spread fast, leaving plants that look ragged and struggle to put energy into producing sprouts. The good news is that most causes are identifiable and treatable once you know what you are looking for.

The Most Common Culprits

Three pests account for the vast majority of holed Brussels sprout leaves: caterpillars (mainly cabbage white and cabbage moth larvae), flea beetles, and slugs. Each leaves a slightly different signature. Large, ragged holes eaten inward from the leaf edge or through the middle of a leaf usually point to caterpillars. Dozens of tiny, neat round holes scattered across seedling leaves are the hallmark of flea beetles. Irregular slime-trailed damage on lower leaves and seedlings is characteristic of slugs and snails.

Caterpillars and What to Look For

Cabbage white caterpillars are pale green and tend to feed on the underside of leaves or deep in the plant where they are hard to spot. Cabbage moth caterpillars are darker and more likely to bore directly into developing sprouts. Check the undersides of leaves for clusters of cream-yellow eggs and remove them by hand. Pick off any caterpillars you find and drop them into soapy water. A fine mesh insect netting over the plants from transplant time onwards is the single most reliable barrier.

Flea Beetle Damage on Seedlings

Flea beetles are tiny black or bronze beetles that jump when disturbed. They favour young seedlings and can riddle leaves with pinhole-sized holes within days of germination. Established plants tolerate moderate flea beetle damage, but seedlings can be set back significantly. Keep seedlings well watered, as stressed plants attract heavier attacks. Covering seedlings with fleece or fine mesh immediately after sowing or transplanting gives strong protection. Neem-based sprays applied in the evening can reduce adult beetle numbers.

Slug and Snail Damage

Slugs tend to feed at night or after rain. Look for silvery slime trails on leaves and around the base of plants. They often chew through the central growing point of young plants, which is particularly damaging. Remove debris and mulch from around plant bases where slugs shelter during the day. Wildlife-friendly iron phosphate slug pellets are effective and safe around pets. Beer traps sunk to soil level capture large numbers overnight.

Ruling Out Other Causes

Hail storms can create similar-looking holes but will affect multiple plants uniformly and typically occur alongside bruised or torn leaf tissue. Wind damage frays and tears leaf edges but rarely creates clean holes. If you cannot find any pest and the holes appear after a severe weather event, damage from the elements is likely and the plants will usually recover on their own once conditions improve.

Keeping Leaves Intact Going Forward

Healthy, well-fed plants grown in fertile soil tolerate modest pest damage without losing yield. The key defences are: inspect plants at least twice a week; use insect-proof mesh from the start; encourage ground beetles and birds which feed on slugs and caterpillars; and remove plant debris at the end of the season to reduce overwintering pest populations. Prevention is far easier than control once a major infestation takes hold.