Common Broccoli pests

The classic caterpillar trio is the imported cabbageworm (velvety green larvae of a white butterfly), the cabbage looper (a green inchworm that arches as it crawls), and the diamondback moth larva (small, wriggly, and green); all chew ragged holes in leaves and burrow into developing heads, leaving dark frass behind. Cabbage aphids form gray-green, waxy clusters on undersides of leaves and in the crown, stunting plants and coating them with sticky honeydew. Flea beetles are tiny black beetles that jump when disturbed and shot-hole young leaves, while cabbage root maggots tunnel into roots and cause sudden wilting of seedlings. Harlequin bugs (shield-shaped, orange-and-black) suck sap and leave pale stippling, and slugs, rabbits, deer, and groundhogs will also graze the foliage.

Common diseases

Black rot is a serious bacterial disease that shows up as yellow, V-shaped lesions along leaf margins with blackened veins, often spreading in warm, wet conditions. Clubroot is a soilborne disease that swells and distorts the roots, causing plants to wilt on hot days and remain stunted. Downy mildew produces angular yellow patches on the upper leaf surface with a grayish, fuzzy growth underneath, favored by cool, humid nights. Alternaria leaf spot appears as dark brown spots with concentric target-like rings, and white mold (Sclerotinia) causes water-soaked stem rot with fluffy white growth; damping-off can also collapse young seedlings at the soil line.

Prevention

Rotate brassicas so they do not return to the same bed for at least three years, and avoid following other cole crops. Space plants for good airflow, keep beds weeded, and water at the base in the morning so foliage dries quickly rather than staying wet overnight. Start with certified disease-free transplants and choose resistant or tolerant varieties where available, and keep soil pH slightly above neutral to discourage clubroot. Clean up and remove crop debris at the end of the season, since many pests and pathogens overwinter in old brassica material and nearby weeds in the mustard family.

Organic control

Cover plants with floating row cover from transplanting to exclude cabbageworms, moths, flea beetles, and root maggots, remembering that broccoli does not need pollination so covers can stay on. Hand-pick caterpillars and egg clusters, and apply Bt (Bacillus thuringiensis) or spinosad to control young caterpillars, reapplying after rain per the product label. Knock aphids off with a strong spray of water or treat with insecticidal soap or neem oil, coating leaf undersides, and encourage lady beetles, lacewings, and parasitic wasps. Use collars or cover soil around seedlings against root maggots, set out slug traps, and for persistent foliar disease pressure a copper-based product labeled for vegetables can help; always read and follow the label for any product you apply.

Scouting & monitoring

Scout at least weekly, checking leaf undersides and the growing crown for eggs, aphid colonies, and small caterpillars before damage becomes severe. Watch for white cabbage butterflies and moths fluttering around the bed, which signals that egg-laying is starting. Inspect seedlings for sudden wilting that points to root maggots or clubroot, and examine older leaves for yellowing margins, angular spots, or fuzzy growth that indicate disease. Pay extra attention during cool, damp spells in spring and fall, when both foliar diseases and pest activity tend to spike.

Tips

Row covers installed at planting are the single most effective tool, stopping most broccoli pests before they ever get established. Harvest the main head before it loosens and yellows, then keep scouting, because side shoots will keep producing and can attract a fresh round of caterpillars and aphids.

General home-garden IPM guidance, focused on prevention and least-toxic control. Always read and follow the product label for any pesticide, including organic products. Page updated Aug 4, 2026.