Pest
Carrot fly
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Watch for | Watch for in May | Watch for in June | Watch for in July | Watch for in August | Watch for in September | Watch for in October | Watch for in November |
What it is
Carrot fly is a small, shiny black fly with a yellowish head and legs, about 8 mm long. It is drawn by scent to carrots and their relatives, and its larvae feed in the roots. Many allotment holders consider it the single biggest obstacle to growing good carrots.
Symptoms
Roots are riddled with narrow, rusty brown tunnels just below the skin, and creamy white maggots up to 1 cm long may be inside them. Damaged roots often rot in storage. In bad attacks, foliage takes on a reddish or yellowish tinge and young plants wilt or die. Holes from slugs or wireworms are wider and lack the rust-coloured tracks.
Cause
The first generation of flies appears in late spring and lays eggs in the soil beside carrot rows. Larvae burrow into the roots, feed for several weeks, then pupate in the soil. A second generation follows in late summer, and its larvae can keep feeding through winter in carrots left in the ground. The females fly close to the ground and find crops by smell, especially after thinning bruises the foliage.
Control
There is little you can do once maggots are inside the roots, so lift and use damaged carrots promptly, cutting away affected parts. Do not leave infested roots in the ground over winter. Dig over the bed afterwards to expose pupae to birds and frost. No chemical treatment is a sensible option for home gardeners.
Prevention
Cover the crop from sowing with insect-proof mesh, sealed at the edges, or surround the bed with a barrier of fine netting about 60 cm high. Sow thinly to avoid thinning, or thin on a still evening and remove the thinnings. Sow in late May or June to miss the first generation, and harvest early sowings by August. Resistant varieties such as Flyaway and Resistafly suffer less damage. Rotate where you grow carrots each year.
Plants often affected
Could it be something else?
These problems share some of the same symptoms. Compare them, or run the symptom checker with these signs ticked.
Months to keep an eye out: May, June, July, August, September, October and November.
Sources
Identification and life-cycle details were checked against the references below. Text and advice are our own. See our editorial policy.