black flies !!!!!!11

[screwbylil]

on our lotties we have noticed our sprouts and most other brassicas are crawling with black flies which are slightly smaller and more delicate looking than a housefly any ides what they are and how to treat ........one leaf alone has 20-30 of the little blighters, they dont seem to be eating anything and just seemed to descend on us one afternoon.

any help appreciated
sue

[SarzWix]

Do they look anything like this picture? I found it via this website, but it seems to be American, so the bug might be called a different name here. If you scroll down the page, it is called cabbage maggot, which I've never heard of!

Resource Guide for Organic Insect and Disease Management

[edit; cabbage root fly is what it's known as in UK]
This site has some useful info; http://www.gardening-naturally.com/a...y_control.html

[rainbowminx]

OMG I have these too! My purple sprouting broccoli and sprouts are covered with bird netting but I have noticed the PSB is covered with loads of tiny black flies, about 3-4 mm long. If I shake the leaf they move about, but soon settle back on. Any more advice from anyone appreciated. Do they need killing? Will they eat my lovingly grown brassicas?!

[SarzWix]

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.

Seems like Enviromesh gets another vote for keeping the pests out!

[rainbowminx]

Thanks Sarah! Anyone any idea how to kill them now they are already there? If I put mesh on them now it will just keep them in!! I try to be as organic as possible but am open to suggestions.

[screwbylil]

thanks so much for that the crop in question was covered when young up to about 3 months the sprouts forming dont seem to be affected time for enviromesh next year, i did use collars as well so it just seems the flies are a nuisance at the moment forwarned forarmed thanks again

[screwbylil]

Do they look anything like this picture? I found it via this website, but it seems to be American, so the bug might be called a different name here. If you scroll down the page, it is called cabbage maggot, which I've never heard of!

Resource Guide for Organic Insect and Disease Management

[edit; cabbage root fly is what it's known as in UK]
This site has some useful info; Cabbage Root Fly and Carrot Fly Control

yep they do havnt seen the pupua stage at all the brassicas have looked lovely and clean till last week when the flies just seemed to come from nowhere, they have had collars on and mesh whilst they where young i only uncovered them about 2 months ago but hey ho im learning not is all rosie in the lottie thanks for your help