Fungus Gnats: How to Get Rid of Annoying Pests in Substrate
Are small black flies circling your pots, and do translucent larvae with black heads occasionally emerge from the soil? Then you are dealing with fungus gnats. These inconspicuous pests can trouble plants more than it may seem at first glance. The adults do not cause damage, but the larvae feed on fine roots, carry pathogens and slow growth. The good news? They can be successfully controlled – with natural and biological methods. We will show you how.
What are fungus gnats and why are they dangerous?
Fungus gnats (Sciaridae) look like tiny mosquito-like flies growing to a size of 1-4 millimetres. Female fungus gnats lay eggs in the substrate, from which translucent larvae with black heads hatch. It is the larvae that cause the biggest problems. They feed on organic material, algae and young roots, thereby disrupting the plants’ uptake of water and nutrients. The result is slowed growth, yellowing leaves and the overall decline of the plants. Fungus gnats also carry moulds and pathogens, which, in combination with a humid environment, can have a devastating effect on your plants.
How do you know that you are dealing with fungus gnats?
An infestation of fungus gnats is not difficult to notice. The main sign is adult fungus gnats flying above the substrate, especially when watering or handling plants. You will find fungus gnat larvae just below the surface of the substrate. If you do not intervene in time, you may notice these symptoms on the plants:
- wilting even when fully watered
- slow growth
- yellowing leaves
Natural methods of controlling fungus gnats
When your garden is infested with fungus gnats, try natural methods first before resorting to chemical sprays. The following proven methods work against fungus gnats:
- Yellow sticky traps: Adult fungus gnats are attracted to the colour yellow. Place yellow sticky traps around the plants and catch as many adults as possible. Replace the sticky traps regularly.
- Let the substrate dry out: Fungus gnat larvae need moisture to survive and thrive in waterlogged substrate. Let the soil dry out thoroughly between waterings to reduce the larval population around the roots.
- Watering with a weak hydrogen peroxide solution: A weak solution (for example, 3% hydrogen peroxide diluted 1:4 with water) helps kill larvae in the substrate. Apply once every few days, ideally only as a one-off treatment.
Products against fungus gnats
Chemical sprays are less effective in the case of fungus gnats than they are with other insect pests, and it is better to get rid of them by natural means. Biological protection and protective bio sprays based on natural oils are effective.
- Biological control against fungus gnats: Parasitic nematodes (Steinernema feltiae), bacteria (Bacillus thuringiensis var. israelensis) and predatory mites, which actively hunt the larvae, are effective against fungus gnats.
- Sprays against fungus gnats: Biocont Na smutnice v substrátu, Agro Natura Smutnice
- Preventive products for protecting plants against fungus gnats: Biocont PREV-GARD, Neem Azal, Rock Effect, CannaCure, BioBizz Leaf Coat, BioNova NovaFoliar, Botano Health
You may also be interested in: How to deal with spider mites, How to deal with whiteflies, How to get rid of slugs
For more advice on how to combat pests and further tips and tricks for indoor and outdoor growers, visit our Higarden blog.