Fungus gnats
Sciarid flies, more commonly known as ‘fungus gnats’, are a fairly common pest on indoor houseplants and are seen more and more due to the increase in houseplant buying.
Fungus gnats live off decaying matter in compost and love warm, moist environments which is why they are rarely seen outside. It is unlikely that these flies were present at the stage of compost production due to the amount of agitation that occurs during the bagging process, but they can make their way into compost bags or potted plants at any time.
The flies become more apparent when plants and compost bags are brought indoors as the higher temperatures will speed up the insect lifecycle. The insects are not harmful to established plants but the larvae can eat roots of seedlings and cuttings.
Treatment and control
- Allow the compost to dry out between waterings. Always conduct a finger test to feel the moisture levels lower down the pot before watering – just in case!
- Don’t ever leave a plant standing in water, always allow it to drain completely.
- To stop the lifecycle of the fly, add a thick layer of fine grit or sustainably crushed shells over the top of the compost to prevent the flies laying their eggs.
- During the warmer months you can give your houseplant a summer holiday by leaving it outside away from direct sunlight. This will encourage the flies to go elsewhere.
- To monitor the numbers and help control you can use FlyClear sticky traps.
- When purchasing a new plant, if you can, quarantine it in a separate room, away from your other plants to see if there is an infestation.
- Open any new compost bags outside if you can and if there are fungus gnats, empty the compost into a shallow bucket and leave outside to allow the flies to move away.
For more information check out fungus gnats (sciarid flies) at the RHS Gardening website.
