How do I treat fungus gnats on Anthurium?

Let the top 2–3 cm of potting media dry completely between waterings — this kills larvae and stops egg laying. Apply Bti (Bacillus thuringiensis israelensis) as a soil drench (mosquito bits work) every 7 days for 3 cycles — kills larvae, harmless to plants and humans. Use yellow sticky cards near the pot to trap adults and monitor population. For severe cases, repot in fresh, well-draining mix and dispose of the old soil.

How do I prevent fungus gnats on Anthurium?

Avoid bagged potting mix sitting open in a humid room — it can come pre-infested. Use a well-draining mix with chunky perlite or bark so the surface dries fast. Bottom-water plants prone to gnats so the surface stays dry.

PEST DIAGNOSIS · CITED TO PENN STATE EXTENSION — FUNGUS GNATS

Fungus gnats on Anthurium: how to identify and treat

How to identify fungus gnats on Anthurium

Adults: small dark flies that flit around the pot and the air just above it. Larvae: tiny translucent worms with shiny black heads, found in the top layer of wet potting mix.

Damage signs to look for

Slowed growth in seedlings and young plants, mushroom-like off smell from the soil, occasional yellowing of lower leaves on small plants. Mature plants tolerate gnats with little damage.

Treatment ladder

Let the top 2–3 cm of potting media dry completely between waterings — this kills larvae and stops egg laying.
Apply Bti (Bacillus thuringiensis israelensis) as a soil drench (mosquito bits work) every 7 days for 3 cycles — kills larvae, harmless to plants and humans.
Use yellow sticky cards near the pot to trap adults and monitor population.
For severe cases, repot in fresh, well-draining mix and dispose of the old soil.

Prevention going forward

Avoid bagged potting mix sitting open in a humid room — it can come pre-infested.
Use a well-draining mix with chunky perlite or bark so the surface dries fast.
Bottom-water plants prone to gnats so the surface stays dry.

Life cycle

Egg to adult in ~3 weeks indoors. Each female lays ~200 eggs. Larvae stay in the top 2–3 cm of media, which is why surface-drying breaks the cycle.

Source

Identification, treatment intervals, and prevention guidance per Penn State Extension — Fungus Gnats. Always follow the product label when applying any pesticide or horticultural oil.