Carrot fly

What is carrot fly?

Carrot fly is a small black-bodied fly whose larvae feed on the roots of carrots and related plants, such as parsnip, parsley, celery and celeriac.

Symptoms

• Rusty brown scars ring the tap roots of carrot and other susceptible vegetables, making them inedible, and susceptible to secondary rots
• When the roots are cut through, tunnels are revealed, often inhabited by slender creamy-yellow maggots up to 9mm (3/8in) long

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Carrot fly larvae tunnel into carrots, causing them to rot.

Cover carrot crops with a fine mesh sheet (available at garden centres) to prevent the carrot fly colonising the crop in the early stages.

Control

Non-chemical control

• Sow sparsely to avoid thinning the seedlings. Female carrot flies searching for egg-laying opportunities are attracted by the smell released when surplus plants are removed
• Late sown carrots (after mid-May) avoid the first generation of this pest; similarly carrots harvested before late August avoid the second generation
• Protect vulnerable crops by surrounding them with 60cm (2ft) high barriers made of clear polythene to exclude the low-flying female flies, or cover the plants with  insect-proof netting, such as Enviromesh. It is essential to practise crop rotation with these methods, otherwise adult carrot flies may emerge within the protected crop from overwintered pupae in the soil
• Choose carrot cultivars that are less susceptible to carrot fly, such as 'Fly Away', 'Maestro', 'Resistafly' and 'Sytan'. These cultivars are less susceptible to carrot fly, rather than being fully resistant
• A mixture of pathogenic nematodes, sold as 'Nemasys Grow Your Own', can be watered into the soil to control the young larvae. This is available by mail order from biological control suppliers

Chemical control

Lambda-cyhalothrin (Westland Plant Rescue Fruit & Vegetable Bug Killer) can be sprayed against the adult stage of this pest. There are no soil-applied persticides available for garden use against carrot fly larvae.

Download

Pesticides for gardeners (Adobe Acrobat pdf document outlining pesticides available to gardeners)

Biology

• The maggots hatch from eggs laid in late May–June and in August-September
• Newly-hatched larvae feed on the fine roots but later bore into the tap roots. The brown scars are where tunnels near the root surface have collapsed
• Two or three generations of carrot fly can develop between late spring and autumn, with the pest overwintering as larvae or pupae