Fungus Gnats

I wondered what the little flies were in my herb pots! There aren't too many at the moment, and I don't want to use any insecticides as I spotted a lacewing on my heated propagator the other evening. I have a small bag of grit that I bought for my succulents, so I might try putting that down in the affected pots.

I'm with the layer of grit method along with sticky traps to get those that are flying.

I had a really bad infestation one year and I believe the grit made a huge difference - advised by Mcdood when I was trying to take dahlia cuttings - still trying by the way ;(

What does the grit do Scarlet?

The grit on the top of the pot stops them laying their eggs in the soil.

Time for an update.
Still pretty horrific with even plants like courgettes which have 3 or 4 true leaves suddenly collapsing with their entire stems eaten out. Others are just totally stagnated as they struggle to grow roots faster than they get eaten. Most of my tomatoes have either died or just about managed their first set of true leaves despite having germinated 5 weeks ago.
Sticky traps have caught nothing.
The pyrethrum is successful against the adults but I'm guessing not the grubs.
It remains unseasonably cold so I still can't move the plants away from each other, out into the ground or the blow away. My living room  is full !
Hey ho! I've had a good run over the last decade and can always buy a few plants even if they're uninteresting varieties  It'll be farmer's market veg for us this year!

How many pots have you got? Is it too much work to take the seedlings out give the roots a quick wash and pot in some fresh compost?

A hundred plus ! A pricked out a load of basil today and rinsed all the roots, and re-did some aubergines last week. Poor little things had lost the main central root.
But I don't have enough compost to re-do everything so I'll start choosing what I really don't want to lose.
I've never known it so bad.

The Garden Myths blog had a post about the best fungus gnat management last month. I generally find his posts to be sensible and evidence-based, and he doesn't accept things just because they are conventional wisdom. He suggests letting the soil dry out as much as possible (without it harming your plants) as the first-line treatment. I've been following that advice with my indoor plants and big bag of compost, and am having a much better year for fungus gnats than I have for quite some time!

Watering from the bottom so the top stays dry does the same/or cover all the pots with a layer of grit. My top tip from Mcdood really helped me one year.
The compost I had came with them - so upsetting as it really knocks them back. I lost loads of plants. Standing outside in the day so it's not so warm may help?

Thanks for the link Proserpina. I suspect they were already in some of my compost, too, Scarlet.

Yes, I do always water from the bottom and have been letting the compost dry out almost completely between watering.

Something I noticed tday in the midst of washing and re-potting, is that the rubbish shredded wood and goodness knows what compost seems to have so much fibrous material that although there are large numbers of gnat maggots they're often not eating the roots but the fibrous matter. Not sure if it is significant, but is interesting and is in line with the garden myths blog. 

The cucurbits are suffering the worst sudden collapse, possibly because the grubs are eating up inside the below ground section of the stems; the plants look a little limp and soft one day and then are horizontal the next! I have no doubt that it is the grubs doing the damage - seeing a large number of them inside the chewed out end of a stem it would be hard to think otherwise.

Everybody has gone outside today - it is warm and a little blowey so that should make life tough for the adults!! I've picked through pots and pots of compost removing the grubs and then left the compost out in a tray to bake dry so that I may be able to re-use it for potting on tougher plants.

I think i have an advantage in that all my plants are headed for the open garden where predators in the soil will deal with the problem. The challenge will be protecting tiny plants from plant predators outside.

A couple of chillies and aubergines put on a spurt over night (well it feels like it!) so there is always hope. Fingers crossed for a long warm autumn.