BCSS - Forum

Hi, I have a lot of pots of lithops seedlings and have noticed sciarid flies (mushroom flies) around them over the past couple of weeks. I put up lots of yellow sticky traps and have caught quite a few of the flies but they seem to be still to be seen on the pots. I have also caught a huge number of larger flies, quite revolting really.

I am concerned for my lithops seedlings most are anything from newly germinated to 6 months old. And wonder what is the best insecticide to use for such small seedlings?. I have some provado concentrate somewhere here which I could use if it won't hurt them.

Any suggestions appreciated, thanks.

I would top-dress between the seedlings with a fine gravel. A physical barrier will prevent the adults laying eggs into the soil. Also, let the soil dry out properly and stay dry for a good few days between waterings, certainly with anything more than a few weeks old.

Don't plant in peat. Cover the top of the soil with something even less inviting than the soil. Better yet, microwave your soil and seal them in plastic bags for the first few weeks. After that you can let the top of the soil dry out and it will be much less inviting.

Once you notice you have the larvae in your soil, then you're in big trouble. Anything still with just a single thin root will rapidly be killed. You could try drenching the soil with Provado (diluted!) although it isn't labelled for that use. Not much point spraying the plants - I'm guessing that letting the grubs kill your seedlings and then be killed by the poison in them isn't what you want?

There are some specific sciarid fly killers just search online and you'll find a few. Personally I've used 'Gnat Off' and found that it works pretty well. 'Gnat Off' contains Bacillius thuringiensis (Bt) and it is this that kills the larvae, indeed I believe that all of the specific sciarid fly treatments do target the larvae - after all it is the larvae that do the damage. I'm not aware that 'Gnat Off' has any effect on plants, it's just a water-based suspension you dilute further with water - I use it on a variety of seedlings and bulbs when necessary but don't actually deliberately spray the plants because it's the soil that needs the treatment.

Make up a solution and give the affected pots a good soak, I just spray the soil, and it should kill the larvae within a couple of days (in my experience), you may see a few flies emerge in the first day or so after the treatment but they should stop soon as the larvae are killed. There may be a little persistence of the bacillus and I have given a second treatment later on if necessary in the same year.

I suspect that most insecticides will kill the flies and a soil drench will probably kill the larvae. When I had a large infestation a few years ago after the Gnat Off was effective in that year I treated a small number that were present the year after by watering with a pyrethroid solution and that worked

graham

Thanks for your suggestions.

It is odd, there is no peat in the compost, it is a mix of Tesco's cat litter, silver sand and coarse grit, but mainly cat litter, with pink horticultural grit on the surface of some and cat litter others. I sprayed and drenched the pots in dilute provado liquid as a matter of urgency this morning after seeing clouds of the flies around the pots. The flies appeared to be killed on contact with the spray, and hopefully the larvae in the compost will have been killed as well.

I know provado spray kills sphagnum moss, and also knocks back drosera plants (sundews) if you use it as a spray, although they are fine if you use the soil drench. Hence my caution before spraying.

I will put more grit around the seedlings as well just in case.

Fingers crossed it does the trick.

mary44 wrote:it is a mix of Tesco's cat litter, silver sand and coarse grit, but mainly cat litter, with pink horticultural grit on the surface of some and cat litter others

Sciarid flies usually lay their eggs on organic matter and I learned the hard way that a top dressing of grit is essential when potting-on seedlings. I'm surprised they have been attracted to your mix. I hope your treatment eradicates they little blighters.

I keep a big Drosera near seedlings. They catch most of them.

Hallo,

S. Hammer suggests a strong breeze to prevent sciarid flies from landing.
I had the problem when the substrate was to humid. Let it dry out. But this advice is in contrast to the treatment with Bacillius thuringiensis, because this works only in humid conditions.
Have a look at the other plants around, thy might be a reason for reinfection, a treatment of the sundew with Bacillius thuringiensis is probably necessary.

Viele herzliche Grüße aus Berlin

Jürgen

Herts Mike wrote:I keep a big Drosera near seedlings. They catch most of them.

I keep a pinguicula in my propagator, too. And try saying that after a packet of wine gums.

MALACHIT wrote:... the treatment with Bacillius thuringiensis, because this works only in humid conditions.

This isn't really true. I will accept that you have to water the soil to add the bacillus so that certainly does mean getting it wet but that need only be as a part of normal watering, that is there is no need for any extra water and, in general, most seedlings are kept reasonable moist . Again the bacillus probably needs a moist substrate to survive but in that it needs to be ingested by the larvae the survival of the bacteria is not a major factor (*).

I think that the strangest issue here is that there are sciarid flies in the first place but while I accept that the larvae will need organic material to thrive that does not mean that the adult females are necessarily that discriminating when choosing egg-laying sites. It may well be that they will lay on any moist material and that could include inorganic particles so perhaps any moist surface is attractive to them.

I certainly have had infestations in my bulbs although they are in a really quite quick draining mix but it does contain coir so I suppose that's sufficient to get them started until they can get to the bulbs themselves. Irritatingly I have had quite a few this year but I am sure that they have come in via some reused growbag compost but I have just treated with Gnat Off and number would appear to be zero or close to it again.

* I am really not sure whether the Bt preparations are actually 'living' and so do grow when added to the soil or are just preserved bacteria. In fact what does the killing are some proteins within the bacteria so the bacteria need to be ingested by the larvae but I suppose the bacteria may be living or dead when eaten.

graham