Kohlrabi: Pests & Diseases
Kohlrabi is a quick-growing brassica valued for its crisp, swollen stem rather than a leafy head. It suits succession sowing in British gardens, but young plants are vulnerable to flea beetles and root fly. Protecting them early produces tender bulbs before they become woody.
Common pests
Flea beetles are especially damaging to kohlrabi seedlings, leaving characteristic shot-holes that can slow growth. Cabbage white caterpillars from large and small white butterflies, plus cabbage moth caterpillars, chew foliage. Mealy cabbage aphid and cabbage whitefly may cluster on leaves. Cabbage root fly maggots cause wilting and poor establishment, while pigeons can graze exposed young plants and strip leaves.
Common diseases
Club root can prevent kohlrabi from forming a good swollen stem by causing distorted roots, stunting and wilt, especially in wet acidic soil. Downy mildew produces pale patches and grey growth below leaves. White blister forms white raised pustules. Powdery mildew may occur on older foliage. Ringspot causes dark circular marks, and black rot leads to yellow margins and blackened leaf veins.
Prevention
Rotate kohlrabi with all brassicas, leaving several years before using the same ground again. Improve drainage and lime acidic soil to reduce club root pressure; choose resistant varieties if club root is present. Sow or plant at sensible spacing, keep beds weed-free and remove diseased debris. Fine insect-proof mesh from sowing or planting is the single most effective protection, excluding flea beetles, butterflies, pigeons and root fly.
Non-chemical control
Cover seedlings promptly with fine mesh and tuck edges into the soil securely. Use brassica collars around transplants to deter cabbage root fly. Hand-remove butterfly eggs and caterpillars from foliage, and squash or wash away small aphid colonies. Encourage hoverflies, ground beetles and small wasps by growing flowers nearby. Keep seedlings watered through dry spells so they outgrow minor flea-beetle damage quickly.
What to look for
Inspect direct-sown seedlings every few days for flea-beetle shot-holes, pigeon grazing and uneven emergence. Check newly planted kohlrabi for wilting linked to cabbage root fly. From late spring onwards, inspect leaves weekly for eggs, caterpillars, aphids and whitefly. Look for mildew and leaf spots after wet weather, and pull up severely stunted plants to inspect roots.
Tips
Harvest when stems are about 5 to 8 cm across, before the flesh turns tough and fibrous. Sow small batches every few weeks for a steady supply. Keep growing plants evenly watered to avoid woody, split stems.
Kohlrabi pests & diseases: frequently asked questions
What are the common pests of kohlrabi?
Flea beetles are especially damaging to kohlrabi seedlings, leaving characteristic shot-holes that can slow growth.
What diseases affect kohlrabi?
Club root can prevent kohlrabi from forming a good swollen stem by causing distorted roots, stunting and wilt, especially in wet acidic soil.
How do I prevent pests and diseases on kohlrabi?
Rotate kohlrabi with all brassicas, leaving several years before using the same ground again.
General guidance for UK home gardens, focused on prevention and non-chemical control. The RHS or a local garden centre can help with tricky cases. Page updated 18 Sep 2026.