black flies !!!!!!11

Cabbage Root Fly
Attacks all members of the family Cruciferae including leafy, heading and root brassicas, and some ornamentals such as wallflower and stock.

Damage on root brassicas is mainly mining of the surface areas of the swollen root, on other brassicas attacks on young plants will cause wilting and death.

There are normally three distinct generations each season in England and Wales and the milder parts of Scotland, but in cooler areas there may only be two generations.

The pest overwinters in the soil as pupa, emerging as an adult fly over a 4-5 week period from mid April in warm areas, and from mid May in cooler areas.

Before laying fertile eggs the female has to feed on pollen and/or nectar, her favoured food plant is cow parsley (Anthriscus sylvestris) and when cow parsley starts to flower, the first generation of cabbage root fly starts.

This means that controls should be in place at the first sign of cow parsley flowers.

The female fly, similar in size and appearance to a house fly, searches for young host plants and lays her eggs on or just below the soil surface normally less than 2 cms from the host plant stem.

If close-fitting collars are in place she cannot lay her eggs near enough to the plants for the hatched larvae to reach the plants. If collars are correctly applied and in good time, cabbage root fly damage will be minimal. Collars are not generally practical or effective on root brassicas.

Covering young crops with fleece or mesh will prevent the fly reaching the crop at all and prevent any damage. Covers are effective on all brassicas.

The second generation normally starts in mid to late June in the south, July in cooler areas.

The third generation starts in mid August, but by this time there will be some overlap of generations.

Although root crops are subject to damage throughout their lives, on heading and leafy crops significant damage only occurs on young plants, so older plants will not need protection.