Fungus gnats

[Cairenn]

Hi guys! So, I have 8 plants in my room, 4 are succulents/cacti, a baby orchid, a large and small Peace Lily, one I cannot really identify (I think it’s a Chinese paddle plant???) and a purple wood sorrel.

My issue is fungus gnats. I thought they were just fruit flies, but I got confirmation from a gardener friend that they are fungus gnats. So, it all started when I was watering the peace lily and noticed that there were little mites in the soil. Straight away I stopped watering my plants because apparently I was doing it too often which attracted the mites. About a week later I noticed some gnats flying around my room.

After a few weeks of doing this, and making sure the soil was completely dry before I watered them again, I still have the fungus gnats. Not as many, but they are there. So, I bought a Bug & Larvae Killer that has Pyrethin in it to use on the leaves and stems, as I can’t find any larvae in the soil.

I’m now finding the gnats hiding out under one of my large leaf succulents. I do not water my succulents often at all since it’s winter time now, so they soil is basically bone dry. Also, the succulents and cacti are in a medium specific to their needs, so there’s no decaying matter like what I have my other plants in.

Please help me get rid of these things, I don’t know what else to do! I’m really at a loss. Apologies for the ridiculous post!

Thanks x

 

[Sheal]

I had a hard time with these some years back. There are usually two ways of picking these gnats up. Either because the plants have been outside at some time or through bought soil or compost. Many of the companies that produce these don't screen/clean the soils now. B&Q's Verve multi purpose compost is one of the worst.

After battling for the best part of two years I took desperate risky measures with my indoor plants. To deal with the larvae I removed all my plants from their pots and soil at the same time, rinsed the roots under a running tap, then immersed the roots in buckets of water to drown the larvae. I put them in a room where the gnats were non existent and kept the door shut. The soil I dampened slightly and microwaved it for five minutes to kill any remaining larvae. A long, time consuming process. Once it had cooled I put it in sealed containers ready for re-use and then I washed all the pots and left them empty.The gnats take up to a fortnight to die so with no access to soil it was a case of waiting. My plants sat in water all that time with no ill effects -surprisingly. Two weeks on I re-potted all the plants with the sterilised (microwaved) soil and they remained clear of both gnats and larvae. An alternative to microwaving is to bake the soil in an oven where larger amounts can be 'cooked' at the same time.

You may want to try this process but it depends on how desperate you are. I can't guarantee the life of your plants either and that's the risk but they are tougher than we think. If changing the soil of your indoor plants in the future it's best to microwave it first in case the gnats/larvae are introduced again.

 

[Cairenn]

I had a hard time with these some years back. There are usually two ways of picking these gnats up. Either because the plants have been outside at some time or through bought soil or compost. Many of the companies that produce these don't screen/clean the soils now. B&Q's Verve multi purpose compost is one of the worst.

After battling for the best part of two years I took desperate risky measures with my indoor plants. To deal with the larvae I removed all my plants from their pots and soil at the same time, rinsed the roots under a running tap, then immersed the roots in buckets of water to drown the larvae. I put them in a room where the gnats were non existent and kept the door shut. The soil I dampened slightly and microwaved it for five minutes to kill any remaining larvae. A long, time consuming process. Once it had cooled I put it in sealed containers ready for re-use and then I washed all the pots and left them empty.The gnats take up to a fortnight to die so with no access to soil it was a case of waiting. My plants sat in water all that time with no ill effects -surprisingly. Two weeks on I re-potted all the plants with the sterilised (microwaved) soil and they remained clear of both gnats and larvae. An alternative to microwaving is to bake the soil in an oven where larger amounts can be 'cooked' at the same time.

You may want to try this process but it depends on how desperate you are. I can't guarantee the life of your plants either and that's the risk but they are tougher than we think. If changing the soil of your indoor plants in the future it's best to microwave it first in case the gnats/larvae are introduced again.

That response! Thank you very very much for the information! I actually might do that. I really love all my plants, and worked hard to make sure they flourished. If it worked, which it doesn’t sound like anything could live after your steps, then it has to work for me. And if I lose a few plants that’s ok if it means I don’t have random visitors in my face all day. Also, I didn’t think about ‘cooking’ the soil before using it. I use BabyBio houseplant compost, but I’ve no idea if they actually do anything to make sure nothing is in it beforehand. I do know that it’s full of decaying plant matter, so there could possibly be tag-alongs in it. Thanks for the advice!

 

[zigs]

Once they've gone, only water from the bottom instead of from above. They live in the top of the soil so if that stays dry they shouldn't come back

 

[Sheal]

You're welcome Cairenn.

@zigs it makes no difference how the plants are watered. The gnats will exist in the soil whether it's wet or dry. I've tried everything with the exception of chemicals and if the gnats are there the larvae will be too.

While we are on the subject of fungus gnats.....a safety issue.

The smoke alarms in my house would give out a blip as if the batteries were low once in a while, or they would stop working completely. By chance I discovered it was the fungal gnats getting inside and setting them off. If you have, or have had the gnats indoors check that the alarms are still working.

 

[Chuck]

If you folks could only get spinosad fungus gnats wouldn't be a problem. Use it as a drench when you water. The bacteria in spinosad kills them.

 

[Sheal]

We can get it here Chuck but it's not cheap to buy.

https://www.ebay.co.uk/sch/i.html?_nkw=spinosad

 

[Chuck]

We can get it here Chuck but it's not cheap to buy.

https://www.ebay.co.uk/sch/i.html?_nkw=spinosad

Good Grief!!! It's 1/3 of that price here. But it is really good stuff. I use it on everything from caterpillars to beetles to stink bugs, but, at that price I will have to start smashing them with bricks.

 

[Sheal]

Living here in the Scottish Highlands I don't need it. I've lived in my present home exactly one year today and apart from the occasional earwig I've not seen any bugs to worry about.....and only two slugs! Fungus gnats won't be a problem either, I've given up house plants.

 

[Cairenn]

Once they've gone, only water from the bottom instead of from above. They live in the top of the soil so if that stays dry they shouldn't come back

Will this work for succulents too? I know most succulents have pretty short root systems. I don’t think they’re in the succulent soil, but I keep finding them hanging out under the leaves and stuff

 

[zigs]

Will this work for succulents too? I know most succulents have pretty short root systems. I don’t think they’re in the succulent soil, but I keep finding them hanging out under the leaves and stuff

Not got any in my succulents