Fungus gnats in polytunnel?

[columbine]

I have raised beds in my poly, the soil of which is a mixture of bought in soil and compost from the local council. The poly is new since June. Now I find that the the beds are covered with tiny little flies, which either crawl away or fly off when disturbed. They have transluscent wings. Could these be fungus gnats? Or what? Are they going to cause damage?
All I have left growing in the poly at the moment are some salad leaves, rocket, etc., some carrots, leeks and sprouting broccoli. I have just sown some chard and perpetual spinach seeds. What should I do to get rid of these little pests, or will they die off in the winter?

[FelixLeiter]

They might be fungus gnats, but then they may be fruit flies. There are a lot of fruit flies around at the moment, while it remains mild. They're benefitting from there being lots of decaying stuff around on which to feast. Fungus gnats can be harmful to plant roots, whereas fruit flies are merely an irritation. Be sure to identify what you have before reaching for the sprayer.

[Nature's Babe]

Hi Columbine ! Maybe hang up some greenhouse yellow insect catchers prevention is better than cure ? I used them last year and had no problems, forgot this autumn and had a few whitefly. Do you cover your compost heap, fruit flies will breed there, covered they can't escape when hatched.

[columbine]

Sorry not to have replied before, been a bit preoccupied with other matters. I still don't know what those flies were but the cold weather seems to have killed off 99% of them. Yes, I have those yellow sticky fly-catchers and they are covered with little beasties. I will now have to wait and see what happens in the spring and hope there are no eggs in the soil waiting to hatch out.
Columbine

[John]

Often these tiny pests, which are more of nuisance than anything else, can be knocked down with a quick whiff of kitchen flykiller. This is not harmful to plants and is a very short lived chemical in daylight. You might need several tries over a few days to get them under control.

John

[columbine]

Thanks for that tip about the fly-killer, John. I will give it a try.
Columbine