Cabbage root fly
A small fly whose white maggots eat the roots of cabbage-family crops and radishes, causing wilting and stunted plants.
Also known as: Root maggot
Symptoms and identification
Young transplants wilt on sunny days, turn blue-grey and may die. Older plants are stunted and yellow. Pulling a plant shows white, legless maggots about 8 mm long on the roots, and radishes and turnips are tunnelled and ruined.
Causes
Adult flies lay eggs on the soil near the stems of brassica plants in spring and again in summer. The maggots hatch and feed on the roots for several weeks before pupating in the soil.
Organic treatment
Remove and destroy affected plants and the maggots. Firm the soil around plants and keep them well watered to help them survive light attacks.
Prevention
Fit a collar of carpet underlay or thick card around the stem of each transplant, or cover rows with fine mesh straight after planting. Rotate crops and plant slightly later to miss the first egg-laying.
Chemical treatment (use with care)
There are very few insecticides approved for home gardens. Prevention with collars and mesh is by far the most reliable.