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undefeatable fungus fly/sciarid fly

my indoor plants have been infested with fungus or sciarid fly since last summer. I bought some peat free compost from a well known home and garden chain to grow seeds and within a couple of days realised they had flies. Since then all my house plants became infested.
I tried hydrogen peroxide to no avail and then mosquito dunks for every water for several weeks. Eventually I threw out the most infested and repotted the others, just keeping the root ball.
I have less of the flies but I do still have them. I just found that my antihurium is still badly infested, another antihurium in my bathroom also seems to have a few flies. I am wondering if these are some sort of super strain or not even fungus flies, although they are not interested in vinegar traps so are not fruit flies.  - any ideas any one?


  • Pete.8Pete.8 Posts: 11,286
    These type of annoying flies lay their eggs in the compost.
    The eggs hatch and feed on organic stuff in the compost then mature into flies and the cycle repeats.
    If you put a decent layer of gravel/grit on top of the compost the flies will struggle to get to compost to lay their eggs so their numbers will start to decline.

    The flies also like damp compost, so try and keep the watering to just enough.

    After a week or so you should see their numbers in decline

    Billericay - Essex

    Knowledge is knowing that a tomato is a fruit.
    Wisdom is not putting it in a fruit salad.
  • wild edgeswild edges Posts: 10,435
    I had the same problem due to Pandemic-grade compost. I suspect companies were rushing to get the stuff out to meet demand. Water from below to keep the soil surface dry. Yellow sticky traps around the plants if you can. I found the traps did better if they were horizontal a few centimetres above the soil surface. The hoover is also a great tool to deal with any adults you see. If you're brave you can do what I did and made a 'Pooter' to suck them up, like the photo below. Google the instructions but they work a treat for removing the sneakier adult flies from among delicate plants.

    If you can keep your head, while those around you are losing theirs, you may not have grasped the seriousness of the situation.
  • Balgay.HillBalgay.Hill Posts: 1,085
    The yellow sticky traps worked for me.
    Sunny Dundee
  • Had the same problem over the summer. Since I'd already got the compost and didn't want to waste it I took to pouring boiling water through it before using it. I appreciate it probably killed the good bacteria and fungi in there too and came out practically sterile but it did give some vaguely useful compost for seeds. But yes we too had some really bad really rubbish compost batches. I grow some things in clear pots so I can see the root development - and could also see the larvae moving around in there. 

    As for getting rid of the flies finding something to cover the soil is good advice, it'll help to break the lifecycle. Some limited success with insecticidal sprays but it sounds like you've tried that. If flies all over the house are driving you mad then could put all the infested plants together in one room until you can get it under control. 
  • Hi
    Thanks for your tips and tricks, unfortunately I have tried most of them in differfent forms!
     I move the pot around and they seem to some out then, so any I find I swat.
    I covered the tops of the soil tightly with cardboard, however I found that the ones that hatched then seemed to burrow their way out of the bottom of the pot and it didn't seem to break the lifecylce, I think maybe because they couldn't get out they laid eggs where they were...
    I have left my plants so dry that the soil is completely dry and I mostly spray with water rather than water pour onto the soil.
    The hydrogen peroxide and mosquito dunks are supposed to kill the larve and may have had some effect but not enough.
    The yellow traps do work, but they are horrible to look at ! and obviously don't catch all of them, leaving some free to complete the lifecycle.
    I was hoping someone had some foolproof anti fungus fly potion or an idea of what else they could be as I only have a couple of house plants left now.

  • Pete.8Pete.8 Posts: 11,286
    I think if you cover the compost with 1/2"+ horticultural grit, very few will be able to burrow down through it to lay eggs.
    Their number will then decline.
    Watering from the base as suggested above will also help a lot.
    Then you can remove the grit if you wish.

    These little flies are all around, all the time - even in mid-winter you'll find them on some rotting fruit.
    So they're not necessarily in fresh bought compost, but they'll soon sniff out an opened bag.
    If I have an opened bag of compost in the greenhouse, then I'll often see them when I open the top.

    Billericay - Essex

    Knowledge is knowing that a tomato is a fruit.
    Wisdom is not putting it in a fruit salad.
  • You can safely use neo-nicotinoids on indoor plants. They are often labelled vine weevil killers. They’ll sort them out. I tried this out of exasperation a few years ago and it worked quite well. Horticultural grit works well as Pete says. You also have the option of trying nematodes (haven’t tried this yet). 

    Just remember not to use neo-nicotinoids on outdoor plants as they can be harmful to pollinators and are long lasting. 
  • I've had good luck with the yellow stick traps, as well.
    New England, USA
    Metacomet soil with hints of Woodbridge and Pillsbury
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