Fungus Gnat Control: Gnatrol vs. Beneficial Nematodes

A gardener asks if Gnatrol (Bacillus thuringiensis israelensis) and beneficial nematodes (Steinernema feltiae) can be used simultaneously for fungus gnats.

Recommendation: Choose One

Using both provides no added benefit. Start with Gnatrol – it's less expensive and more available. If ineffective, try nematodes.

Address Root Causes

Fungus gnats thrive in:

• Poor quality or contaminated potting soil
• Unnecessary repotting (new soil often contains larvae)
• Consistently moist soil surface

Effective Cultural Controls

1. Remove all loose surface soil not touching roots – this is where larvae concentrate.
2. Allow soil to dry deeply between waterings – dry soil kills larvae.
3. Avoid overwatering and pots without drainage.

These steps alone often resolve infestations without chemicals.