Latin name: Bradysia spp. and Sciaridae spp.
Fungus gnats are small flying insects commonly found in greenhouses, nurseries, indoor plants and propagation areas throughout Australia. They thrive in damp, organic-rich growing media where fungi and decaying plant material are abundant. While adult fungus gnats are primarily a nuisance, their larvae feed on fungi, algae and fine plant roots, making them particularly damaging to seedlings, cuttings and young plants.
Fungus gnats are most active in warm, humid conditions where potting media remains consistently moist. Overwatering and poor drainage can quickly lead to large infestations.
Lifecycle
Fungus gnats complete their lifecycle in around 3–4 weeks under favourable conditions.
- Adult females lay eggs in moist potting media.
- Larvae hatch and feed on fungi, organic matter and fine roots.
- Larvae pupate within the growing media.
- Adults emerge and begin reproducing within a few days.
Continuous moisture allows multiple generations to develop throughout the year.
Identification
- Adults measure 2–4 mm long
- Slender black or dark grey body
- Long legs and clear wings
- Weak, erratic flying around pot plants and propagation benches
- Larvae are translucent white with shiny black heads
- Commonly found on or just below the soil surface
Damage
- Root feeding weakens seedlings and young plants
- Reduced germination and poor establishment
- Wilting despite adequate moisture
- Larvae can spread root diseases such as Pythium and Fusarium
- Adults become a nuisance in greenhouses and indoor growing areas
SOLUTIONS
In propagation trays and seedling nurseries: Apply Eco-Neem Organic Insecticide as a soil drench to help suppress larvae while allowing the growing media to partially dry between watering.
Around indoor plants and greenhouse benches: Install Insect Glue Traps to monitor and reduce adult fungus gnat populations. While they won't eliminate larvae, they are highly effective for early detection and ongoing monitoring.
In heavily infested container plants: Combine Eco-Neem Organic Insecticide with Insect Glue Traps to target both larvae and flying adults as part of an integrated management program.
Where persistent infestations occur: Reduce irrigation frequency, improve drainage and remove decaying organic matter to disrupt the fungus gnat breeding cycle before retreating if necessary.
References
https://stratagreen.com.au/products/insect-glue-traps
https://stratagreen.com.au/products/eco-neem-organic-insecticide-250ml
