Controlling Fungus Gnats


Fungus gnats or soil gnats what every you may call them they are one of the most common pests for those starting seeds indoors.

Fungus gnats are small, winged insects that infest soil, potting mix, or plants grown in pots.

Adult fungus gnats don't harm full size plants or people, but they can be annoying.

The adult female can lay up to 200 eggs in her short lifetime and can create a more severe problem.

The adult female lays the eggs in the soil close to soil surface during the single week she’s alive. The eggs hatch and the larvae burrow down into the soil.

Larvae are whitish to clear with black heads and, with a length of less than ¼ inch, very difficult to see. When abundant, they may leave shiny trails on the soil surface


The newborn fungus gnat larvae live in the soil and feed on fungus, organic matter or young roots and can be damaging when their numbers are very high. They can be a cause for young seedlings wilting.

Fungus gnats love damp organic matter, which happens to be the preferred media for your plants too.

The easiest way to interrupt the fungus gnat life cycle is to let soil dry out between waterings. This is not always possible when starting seedlings since they need the moisture to germinate. For seedlings that have established roots systems changing watering practices may solve the fungus gnat problems. It is recommended to allow the soil surface to dry between watering and keeping infested plants away from clean ones.


You next option is to use diatomaceous earth as it is an effective remedy against fungus gnats.


Always use food-grade diatomaceous earth, as the pool grade contains high levels of silica.


Allow the soil mix to dry out before applying the diatomaceous earth to the surface of the soil, as it loses its effectiveness when wet.


With the diatomaceous earth on the soil surface when the adult fungus gnats land on the soil surface or the young larva attempt to break through the soil, the diatomaceous earth covers them in cuts from the sharp shells edges that make up diatomaceous earth material and will soon kill the larva.

The safest and often most effective products for home use are the commercially available biological insecticide Bacillus thuringiensis subspecies israelensis (Bti) that is used to treat bird batch and water features to prevent Mosquito larval from growing into the adults.

Bacillus thuringiensis ssp. israelensis is the most common of these products on store shelves. Mosquito Bits and Gnatrol are common trade names


This Bti is not the same as a Bacillus related product used for caterpillar control on plants such as cabbage and broccoli, repeat applications are often needed for long-term control.

The last method of control is by using sticky material on yellow-colored traps to capture the adults. Fungus gnats have positive phototaxis or in simple terms are attracted to light. The yellow color of the traps is attractive to the adults and the sticky covering traps them when they land.


By capturing the adults and limiting the number of eggs they can lay the fungus gnat population can be controlled.


Happy Hunting.

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