Buzz Off: Sciarid Fly Nematodes

Last year I started overwintering plants in style – or at least in quantity. As I discussed in Overwintering Tea, Coffee and Other Tender Edible Perennials a couple of weeks ago, this year there were even more tender plants knocking on the door once autumn’s hoary fingers reached our garden. I did seriously consider whether or not to overwinter chillies this year, but my tree chillies only started to fruit last week and with so many other tender plants to bring in, I decided to choose a selection of chillies to bring in as well.


My first rocoto tree chilli – ‘Albertos locoto’

Two Sticky Issues – Greenfly and Sciarid Flies

I had a problem with greenfly in early spring last year and never really found a successful way to deal with this problem, so I’m not looking forward to a repeat of the sticky insect invasion this year. Any ideas on ways to deal with this would be most gratefully received. (I did use organic sprays and sticky traps to try and control them). But the main problem I had initially was with sciarid flies or fungus gnats. These are often also a problem with house plants – especially when the compost is high in organic matter like the green waste in the peat-free compost I currently use. (I have used other peat-free compost like the superb Dalefoot wool compost, especially in spring when I’m bringing a lot of seedlings into the house, but can’t stretch the budget to afford it for all my plants at the moment. Besides which, the plants often get infested with sciarid flies in the greenhouse in the summer anyway.) The sciarid fly larval stage can attack the roots of plants, but my main issue with them is the annoying clouds of flies in the house over winter. Conventional tricks to avoid them are to avoid overwatering and water from beneath, but I didn’t find this helped much. I also tried covering the compost with gravel, but this had very little impact on fly numbers.


Return of my little ‘friends’…

Biological Control

So last year I tried nematodes (microscopic worms) as a way of controlling the flies. I’ve previously used nematodes outside very successfully to control pests like vine weevil in pots, but had never tried them in the house. The nematodes worked in about a week and my plants were fungus gnat free for the rest of the autumn and winter. As long as no other plants are introduced into the house with fungus gnats to re-infest cleared pots, this should be a one off treatment each autumn. This year I was sent a free pack of nematodes to trial by The Green Gardener and I treated my plants at the end of last week.


First tray of plants in the bath ready for nematode treatment – bit like sheep dipping

It doesn’t take long to apply (unless you drop a tray of cacti on the floor like I did and thus need to get the vacuum cleaner and cloths out…) The compost needs to be moist before application and the house above 10ºc, with pots out of direct sunlight. One pack (costing £12.50) treats up to 15 sqm of compost – far more than I needed even for 5 full trays of plants, but the solution with the nematodes in can’t be made too strong, so as long as there isn’t more than 15sgm to treat, one pack is ideal.


Small pack – big results

Once again, my pots were cleared of flies within the week and I hope to keep them that way until it’s time for the plants to return to their summer homes. Now I just need to crack the greenfly issue and I’ll have this overwintering lark sorted…

If you’d like to try nematodes to keep sciarid flies off your houseplants, the product can be found on here on The Green Gardener’s website…

Product Reviews

Just a note on product reviews on the blog – I’ve discussed many plants and products over the past few months which have not been free trials. Any reviews of free products or plants will always be a reflection of my honest experiences, good or bad. I don’t review anything which I don’t consider to be of use to my readers and only choose products which I already use and find helpful, or those which I want to try as part of my ongoing garden and allotment development. I will always make it clear where a product has been sent free for me to trial and I hope that the reviews will be useful for other gardeners.

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4 thoughts on “Buzz Off: Sciarid Fly Nematodes

  1. Emma Cooper says:

    I’ve never found the watering advice helps very much, either, and I resort to a bottle of biological control – the kind of thing that is marketed to *ahem* hydroponic gardeners. It works reasonably well until it wears off. Yellow sticky traps are also good, if rather disgusting. Carnivorous plants like sticky Drosera and pitcher plants can help (the little buggers aren’t large enough to trigger a venus fly trap).

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