[shokkyy]

Because the topsoil I bought to fill my new veggie bed this year came infested with them. I noticed them right away, long before I planted anything in it, and they've clearly been multiplying since then. Will they be doing any harm to my plants in there? And is there a way to get rid of them without chemical insecticides, and preferably without harming any good bugs either? They're driving me nuts.

I did Google them and found conflicting opinions, with some people saying they were harmful and others saying they were harmless, some people saying nematodes work and some saying they don't. Obviously laying down a surface mulch of sand or grit like you could for houseplants isn't an option, and nor is not watering my veggies.

[shokkyy]

I'm bumping this up in the hope that someone will see it who can help me out with some advice here. I've seen so much conflicting info on a Google that I'd really like to hear from someone who has real experience of dealing with these critters.

[8doubles]

I have never seen any damage by fungus gnats, i think the compost itself is where all breeding and feeding takes place.
A cheap UV fly killer lamp placed next to the pots at night sorted the annoying beasties out for me.

[Paul Plots]

Quoting shokkyy "topsoil I bought to fill my new veggie bed this year came infested with them"

So a UV lamp won't solve the problem out in the garden but you may well find the change of environment will naturally and eventually dissuade them.

I think they like warm, damp sheltered places to breed in profusion. Being out in the open may well reduce their numbers quite rapidly as it will be draughty, colder over-night and certainly not sheltered. I imagine there will also be a number of predators.

As for damage to plants… not sure but if I see signs of them in the greenhouse it usually means something is a little too wet so I don’t view them as a welcome sign. Easing off with the watering indoors can help reduce them.

[savbo]

the larvae cause a lot of damage to the fine root hairs - I've had many plants stop growing in pots because of them. I've never come across them outside before though. The main non-chemical way of dealing with them in pots is to stop watering from above, but unless you have some pretty special contacts you won't be able to organise that...

[Paul Plots]

the larvae cause a lot of damage to the fine root hairs - I've had many plants stop growing in pots because of them. I've never come across them outside before though. The main non-chemical way of dealing with them in pots is to stop watering from above, but unless you have some pretty special contacts you won't be able to organise that...

    
Heaven forbid.... we've only just had rain here after weeks and weeks of needing it.

[shokkyy]

Thanks for that. It seems to me there's more of them now than there was when I first put the topsoil down, so if anything I think they're increasing. Obviously there's nothing I can do about rain, but once that stops (if ever) I'll have to see if I can think of ways of reducing water on the surface. I've got a bit of everything planted in there because it's quite a big bed, and I have just been zapping the lot with a hose.

Nobody had any experience of using the nematodes for them? I found one on my Google search called steinernema feltiae which targets fungus gnats and is suitable for outside use, but they're not cheap so before splashing out I'd like to know how effective they are. I'm not keen on using stuff like sticky traps or insecticides because they're going to take out good bugs as well, and I'd rather not eat veggies that have been touched by insecticides.