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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.
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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?
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
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.
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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.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
Growing a mixed collection of cacti & other succulents; mainly smaller species with a current emphasis on lithops & conophytum.
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.
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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 (*).MALACHIT wrote:... the treatment with Bacillius thuringiensis, because this works only in humid conditions.
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.