Carrot Root Fly
On Crops: Carrots, parsnips, celery, caraway, dill, fennel, parsley
Most temperate climates where carrots are grown
Carrot root fly are not often seen in the adult stage. They are slender, small black-bodied flies with yellow legs and large eyes. Larvae are creamy yellow, tapering maggots, up to 9mm long and mainly found in tunnels in roots.
After hatching from eggs that are laid just under the soil surface, the carrot root fly maggots initially eat fine root hairs before tunnelling into the roots. The tunnels are filled with rusty brown castings, or can be seen as excavated grooves. Plants are stunted but seldom killed, but roots are often deformed. Injuries to the roots can then allow disease organisms to enter. After harvest, maggots can still feed and develop in stored roots.
To provide protection, grow plants in a different location to where infected plants were grown previously and cover seed beds with horticultural fleece before seedlings emerge. Make sure to bury the edges under the soil and leave crops covered until harvest. Otherwise, enclose the carrot bed with a vertical fence of window screening, which keeps the adult flies from finding plants. Harvest autumn carrots and other susceptible plants early, and avoid leaving them in the ground over winter. Clean up and discard any plants that may still be around that carrot root flies like.
Harvest promptly to minimise damage.
Where possible, turn over the soil regularly after an infested crop has been removed as this enables birds to eat the overwintering larvae and pupae. Avoid thinning susceptible crops as this will release chemicals that attract carrot root fly. Try growing resistant varieties like `Flyaway’ and ‘Resistafly’.