⚠ ModeratePothos Fungus Gnats — Larval Root Damage from Bradysia spp.
Commonly affects: Epipremnum aureum — Pothos in moist, organic-rich substrates
Tiny black flies (2-4 mm) hover around the pot and fly up when the plant is disturbed or watered. The plant's new growth slows and leaves yellow despite seemingly adequate care. Larvae in the substrate are 4-6 mm long, white with a black head capsule, and feed on organic matter and young roots. In heavy infestations, larval root feeding mimics root rot — the plant wilts and yellows because the root system is physically damaged. Pothos in moist, peat-rich substrates are particularly susceptible.
Potential Causes
- 1Consistently moist substrate surface providing ideal egg-laying conditions for female Bradysia flies
- 2Organic-rich substrates (peat, coir, bark) providing abundant larval food sources
- 3Introduction from infested nursery plants, potting mix, or compost containing eggs
- 4Overwatering maintaining substrate moisture that allows larval populations to build without periodic dry-down interruptions
Solution Steps
- 1Allow the top 5-7 cm of substrate to dry completely between waterings — this kills eggs and early-stage larvae, which cannot survive desiccation.
- 2Apply Bacillus thuringiensis israelensis (Bti) as a drench every 7-10 days for 4-6 cycles. Bti is a biological larvicide toxic only to Bradysia larvae.
- 3Apply Steinernema feltiae nematodes as a soil drench — these parasitise fungus gnat larvae with high efficacy.
- 4Place yellow sticky traps at soil level to catch and monitor adult gnats.
- 5Top-dress the substrate surface with a 2 cm layer of dry coarse sand or perlite — this deters female gnats from ovipositing in the substrate.
- 6Reduce watering frequency as a long-term preventive measure.
Prevention Tip
The single most effective fungus gnat control for Pothos is allowing the substrate to dry to 5-7 cm depth between waterings. This habitat modification disrupts the larval lifecycle without any chemical intervention.
