Hi all

Didn't turn up anything on Google on this one, except an unanswered query in
a longer post about Banana plants. Wonder if anyone can shed light on this.

I have had tiny flies (3-4mm, with wings held back along the body)
skittering about on the surface of some of my pots for some time -
especially the wetter ones (I have some carnivorous plants, sundews and
butterworts) and the peat-free compost. I have had a suspicion they may have
attacked the roots of some plants which have failed suddenly.

I came back from holiday to find the peat-free pots and growbags (so
assiduously watered by my neighbour) absolutely heaving with them. I put
down yellow sticky cards at ground level and they were black within an hour.
I also moved pots of sundew and butterwort to ground level and they've had a
huge feast.

The peat-free compost is B&Q's made from composted wood - can be quite
fungusy.

So what are these flies? Are they 'fungus gnats' (in my insect book these
are larger, about 7-8mm)? Why am I attracting/culturing them? What can I do
to control them - and are they causing damage?

Michael S
(urgling again after spending far too much time sorting out a new kitchen)

Michael Savage wrote:
Hi all

Didn't turn up anything on Google on this one, except an unanswered query in
a longer post about Banana plants. Wonder if anyone can shed light on this.

I have had tiny flies (3-4mm, with wings held back along the body)
skittering about on the surface of some of my pots for some time -
especially the wetter ones (I have some carnivorous plants, sundews and
butterworts) and the peat-free compost.

Cannot answer you question but I'd like to know too. Since I repotted
some of my house plants with peat-free compost, my flat is infested!

Philippe

In ,
Philippe Gautier typed:
Michael Savage wrote:
Hi all

Didn't turn up anything on Google on this one, except an unanswered
query in a longer post about Banana plants. Wonder if anyone can
shed light on this.

I have had tiny flies (3-4mm, with wings held back along the body)
skittering about on the surface of some of my pots for some time -
especially the wetter ones (I have some carnivorous plants, sundews
and butterworts) and the peat-free compost.

Cannot answer you question but I'd like to know too. Since I repotted
some of my house plants with peat-free compost, my flat is infested!

Philippe

From another source:

Question: I keep getting little flies on the soil of my houseplants, what's
the cause and can I stop it. I use a multipurpose compost to plant them.

Answer: Those little flies are known as fungus gnats. Annoying, aren't they?
Generally, they result from too much water. Consider watering less often,
especially for foliage plants. If you can't water less, as in the case of
plants that must stay moist at all times, get out a fork and aerate the top
of the soil so the top dries out faster.

other sources say let the compost dry out between waterings.

pk

"Michael Savage" wrote in
message ...
Hi all
I have had tiny flies (3-4mm, with wings held back along the body)
skittering about on the surface of some of my pots for some time -
especially the wetter ones (I have some carnivorous plants, sundews and
butterworts) and the peat-free compost. I have had a suspicion they may
have
attacked the roots of some plants which have failed suddenly.

The maggots of these sciarid flies can damage the roots of pot plants (I
lost a venus fly trap to them, they ate the bulb)
Apparently that new vine weevil killer (Provado) will see them off and I
have treated my pot plants with it. So far I have not been plagued with the
little beggars.

Lisa

On Thu, 12 Jun 2003 10:16:32 +0100, Michael Savage wrote:

I have had tiny flies (3-4mm, with wings held back along the body)
skittering about on the surface of some of my pots for some time

So what are these flies? Are they 'fungus gnats'

Probably.

Why am I attracting/culturing them?

Moist decaying organic matter.

What can I do to control them

I have found the ordinary pyrethrin spray sold for use on
houseplants gives good control of the adults. If you spray
regularly -- once a week, perhaps? -- as further larvae mature
and adults emerge, you have a good chance of totally eradicating
them.

and are they causing damage?

I've read that their larvae nibble growing tissues, but don't
quote me.


--
Rodger Whitlock
Victoria, British Columbia, Canada

Michael, sounds like you've got sciarid fly. its their larvae that damage the roots, the adult flies don't cause any damage at all except for being unsightly. during warmer months there is a bio-control mite readily available from organic gardening cataologues. but these don't work in colder weather. most sites will tell you that there isn't a chemical registered to kill them, but you can make a completely organic one using (can be bought, but is expensive) Feverfew (Tanacetum parthenium) flowerheads - the chemical in them is PYRETHRIN - it basically kills any creepy-crawly it comes into contact with so be careful if other beneficial beasties are present. dry the flowerheads, grind them up, mix with water & washing-up liquid (use an ecologically-sound one), spray. treatment may need repeating on a weekly basis as the larvae turn into adults, but should help get things under control. I understand that your plants like being damp, but try not to over-water & consider watering from underneath as this may have an effect; as far as i know its not anything to do with the compost source/type
hope this helps - wendy

Yes, sciarid fly also known as fungus gnats.

The grubs are about half a cm long, sort of translucent white. Although they eat mainly rotting vegetation, they seem to like soft fleshy roots (eg those of bulbs and cacti), and in abundance can kill the plant. The flies you see will have just 'hatched out' from the grub, so worth squashing as many of them as you can before they go off and breed in another pot. They're fairly easy to squash as they tend to crawl round and round the pot, rather than flying around.

They like damp high humus conditions, which is why you're getting them in damp peat free compost. So, what you can do is:

Kill off any adults by squashing or pyrethrum (but beware beneficial insects)
Consider repotting choice and vulnerable plants in fresh compost.
Cover pots with a layer of dry sand so the soil surface is not attractive to females.
Go over to using soil based composts for a season until you have the plague under control.
Enclose pots of seeds in plastic bags as a physical barrier against the flies
Keep your compost away from the plants, and with the top firmly closed, so that the compost doesn't become infected with them.

By chance, I've found that Nicotiana sylvestris is a useful control in the growing season - the flies are attracted to and get stuck on the sticky leaves and stems, so I grow a few amongst my other plants (Unfortunately whitefly are also attracted to the Nicotiana, and they are strong enough to be able to fly off again))