Sciarid Fly and Shore Fly
The adult sciarid flies live on and around the compost surface of pots, generally
inside rather than outside. The flies themselves are an unsightly nuisance but most
of the damage is caused actually by their young. The small white larvae live in
the compost and feed on the tender roots of plants and cuttings. In our own nursery
we have seen them nibbling at the edges of banana seeds, and preventing germination.
There are two possibilities for biological control of sciarid. Both attack sciarid larvae. One is a predatory mite which crawls over the soil looking for prey, and the other is a nematode which is watered on, and which attacks the sciarid larvae underground. The mites have the advantage that they can crawl into crevices and onto surfaces that the nematodes can't reach. They are also good as a preventative measure, as they can survive with little food, or alternative food. On the other hand the nematodes are more effective if the sciarid population is high. Use both in a two-pronged attack!