Carrots: Pests & Diseases
Carrots are dependable root crops when sown into deep, stone-free soil, but their scent attracts the notorious carrot fly. Fine foliage can conceal trouble until roots are lifted, so prevention matters most. Successional sowings provide fresh roots over a long season and reduce the impact of setbacks.
Common pests
Carrot fly is the main pest: its larvae tunnel through roots, leaving rusty-brown tracks and making carrots bitter or prone to rot. Aphids can colonise foliage, including willow-carrot aphid, which may distort leaves and spread viruses. Slugs sometimes graze seedlings or roots near the surface. Wireworms and carrot weevil are less common local problems, especially in recently cultivated grassland or neglected ground.
Common diseases
Carrot fly damage is often followed by secondary rots, but cavity spot is a separate problem that creates small sunken lesions on roots. Sclerotinia can cause soft, watery decay with white cottony mould during storage or wet weather. Alternaria leaf blight may darken foliage. Forking is not a disease, but is common in stony, compacted or freshly manured soil and spoils root shape.
Prevention
Use deep, stone-free soil that has not recently received manure, and avoid compacting it before sowing. Rotate carrots away from previous carrot, parsnip and celery beds. Cover crops with fine mesh or fleece from sowing, or use a barrier about 60 cm high against low-flying carrot fly. Thin in the evening, remove thinnings immediately, water consistently and choose carrot-fly-resistant varieties where available.
Non-chemical control
Keep fine mesh or fleece securely over carrots, taking care to seal edges against carrot fly. Hand-remove slugs and use physical barriers around vulnerable seedlings. Encourage ground beetles, hoverflies and ladybirds by maintaining diverse planting nearby. Lift and discard severely fly-damaged roots rather than leaving them to rot in the bed. Harvest mature roots promptly and store only sound, dry carrots in clean containers.
What to look for
From late spring, watch young foliage for aphids and inspect seedlings for slug grazing. Check for carrot fly after thinning or windy weather by looking for reddening leaves and rusty tunnels on a test root. During wet spells and before storage, examine roots for sunken spots, soft rot or white mould.
Tips
Sow little and often for a steady harvest, rather than raising one large crop. Avoid bruising roots when lifting, as damaged carrots store poorly. In known carrot-fly areas, choose a breezy exposed bed as well as using a barrier or fine mesh cover.
Carrots pests & diseases: frequently asked questions
What are the common pests of carrots?
Carrot fly is the main pest: its larvae tunnel through roots, leaving rusty-brown tracks and making carrots bitter or prone to rot.
What diseases affect carrots?
Carrot fly damage is often followed by secondary rots, but cavity spot is a separate problem that creates small sunken lesions on roots.
How do I prevent pests and diseases on carrots?
Use deep, stone-free soil that has not recently received manure, and avoid compacting it before sowing.
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.