East of Scotland Begonia Society

Sciarid Fly

or Fungus Gnat

Adult Fly

               These are the small flies around 2mm long, which are usually black in colour and are extremely common, usually present around most house and greenhouse plants they always seem to become more of a problem when you are taking cuttings and the compost is being kept more damp this gives them the perfect conditions for multipyling.

              Because they can breed readily there will be many overlapping generations all year round on indoor plants, each female fungus gnat can lay up to two hundred microscopic eggs after mating The eggs are laid into soil around the base of the plant, and hatch after five to seven days. At room temperature, newly hatched larvae will develop into adults in 20 to 25 days but during hotter times of the year in greenhouse, the life cycle can be as short as one to two weeks.

             The larvae are no more than 1mm long when they first emerge, but can grow to ten times that before pupating the larvae are difficult to see with the naked eye due to their small size and translucent bodies.

They will hide beneath the soil surface where it is moist, and feed mostly on dead organic matter but can damage seedlings and the base of soft cuttings, completely eating them away this level of severity is always in a pot that is far too wet as can be seen below.

          Larvae can also survive on patches of mould on greenhouse floors and benches so practice good plant hygiene this can go a long way to help in the control these pests.

Allowing the soil to partially dry out may help to reduce the larval population in pots.

If you wish to control sciarid flies you can try any of the following. 

         Products containing the following chemical ingredients are all effective on

Sciarid Flies.

                                    Pyrethroids and Pyrethrin

           The parasitic nematodes Steinernema Feltiae can be watered into infested soil.  These are naturally occurring parasites and will infect sciarid larvae with bacteria and kill them.


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