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.
Shore flies live in or on algal scum or very wet, decomposing organic matter and are common in greenhouses and outdoor areas where conditions are damp. They are commonly found buzzing around compost heaps. Their larvae do cause damage, but they are not nearly such a threat as the sciarid fly larvae. Adults are thought to carry pathogens such as fusarium. They are susceptible to the same controls as sciarid fly (see below).
Biological ControlsThere 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!
These are tiny brownish crawling beneficial mites (hypoaspis miles) which eat eggs and larvae of Sciarid flies. The soil temperature needs to be above 12°C, and they will be even more effective if the soil is warmer than that. Use as soon as possible after receipt, and within 48 hours. Store at 15-20° C until use. Keep out of direct sunlight. For more information about hypoaspis mites click here
These are tiny transparent worms (eelworms) which live in the soil. These nematodes are active at temperatures as low as 8°C, but the bacteria that they use to kill their hosts are not, minimum soil temperatures need to be 14°C for the nematodes to work effectively.
The nematodes which are bred to kill leatherjacket larvae Steinernema feltiae are also effective in controlling sciarid fly larvae. For more information about nematodes click here