How to get rid of fungus gnats

The complete guide

Fungus gnat

Difficulty Low

Frequency High

Reproductive rate Up tp 300x

Lifecycle Up to 20 days

Fungus gnats are small dark brown flies whose larvae feed on decomposing organic matter in moist soil. Although they do not directly attack plants, heavy infestations can lead to diseases and root damage.

All plants

Greenhouse plants

Tropical plants

Identifying fungus gnats

Fungus gnats are easily identifiable as they fly near the soil. If in doubt, disturbing them by gently shaking the plant will make them easier to spot.

Early infestation

A few flies present around the soil

Advanced infestation

Many flies present around the soil

Treatment options

Indoor plants

Small greenhouses

Prevention

You will need :

Sprayer
Yellow sticky traps

Natural predators :

Nematodes for fungus gnats

How to treat fungus gnats?

The most effective and safe strategy is to temporarily space out watering to reduce soil moisture and introduce nematodes that attack larvae in the potting soil before they mature. Yellow sticky traps help reduce the adult population.

1

Preparation

Removing debris from the soil of a tropical plant

Remove debris

Remove dead leaves and other debris that may interfere with the treatment.

Installing a yellow sticky trap in a tropical plant

Install the sticky traps

Install the yellow sticky traps to control adult fungus gnats.

2

Nematodes

Introduce the nematodes

Introduce a quarter of a nematode package at each watering for four waterings.

A few important points

Since winged adults easily escape cleaning, contact insecticides, and predators, treatment must target the larvae over a period of at least one month to cover a full life cycle.

Once the treatment is complete

Use yellow sticky traps to confirm the success of the treatment. If new fungus gnats are detected, extend the treatment. Otherwise, you can consider your treatment successful. We recommend using the preventive treatment to avoid a new infestation.

Do I absolutely need to treat all my plants?

Fungus gnats spread quickly, and the absence of symptoms does not mean the plants are healthy. It is therefore strongly recommended to treat all plants simultaneously.

Is it necessary to replace the substrate to treat fungus gnats?

We do not recommend replacing the potting soil. Temporarily removing the eggs and larvae of fungus gnats from the substrate provides little benefit compared to the stress it causes to the plant.

Is diatomaceous earth effective against fungus gnats?

The effectiveness of diatomaceous earth is limited because its action does not last long enough to cover a full life cycle of fungus gnats. Note that it is also incompatible with the use of predators.