Common name: Fungus fly
The adult flies are capable of transmitting plant diseases, and their larvae feed on plant roots, which can check growth and sometimes lead to the plant’s death.
They are attracted to organic matter in the growing media and decaying plant tissue.
It has even been suggested that they are particularly attracted to media containing composted material, which is understandable as home made compost is often just that i.e. decaying plant material.
They are especially troublesome in the warm, humid environment of the greenhouse where life cycles are quick to complete.
Adult flies are 3-4 mm long black flies with long, tapering antennae.
They lay their eggs in moist potting media or where wet patches of soil have perhaps has accumulated after falling from work benches.
The larvae feed for about four weeks before pupating.
Larvae are legless, translucent, 6-10mm long, and have dark shiny heads, and live in the top few millimetres of compost,making them difficult to find.
They feed on the roots of cuttings and seedlings.
A number of things can be done to prevent infestations, for example;
Water from the base of the pot this keeps the top surface of the compost relatively dry.
Topdress the compost with a mulch of grit / gravel/Clay pellets.
Keep capillary matting clean.
Hang up sticky yellow cards or roller sticky fly traps.
The predatory mite hypoaspis, will feed on the larvae in the surface layer of the soil or growing media.
They are a good choice for a preventative treatment or low levels of infestation.
They require a minimum temperature of 10°C(50°F) for the mites to be active and for the eggs to hatch.
Providing the right temperatures are maintained they can survive for several weeks.
The parasitic nematode steinernema also attacks the larvae, including those that have tunnelled into stems.
Apply as a drench when compost temperature is above 10°C (50°F).
Adults and larvae of the predatory Rove Beetle atheta coriaria, eat the adult fly.
The advantage of using this predator is that both the beetle and the larvae are predators, and are effective over a range of temperatures.