They can be controlled by Hypoaspis miles or the biological larvicide Bacillus thuringiensis (subspecies israelensis) that kills the gnats in their larval stage, which must be applied weekly as a soil drench for 4-5 weeks. Detergents and the nicotine from tobacco brewed into a toxic tea are used by some people to control fungus gnats. Another effective deterrent is a yearly bath in insecticidal soap and applying an indoor mulch to the top of your soil. Another organic repellent is the use of Neem oil as a soil drench (diluted 1 teaspoon per litre of water and applied 300 ml per square meter of soil ).
In houseplants the presence of fungus gnats may indicate overwatering. They may be feeding on roots that have sat in drain water too long and are rotting or may be attracted to fungus growing in saturated top soil. Limiting moist environments and allowing the soil to dry will reduce their numbers. Fungus gnats are typically harmless to healthy plants, but can inflict extensive damage to seedlings; their presence can be indicative of more serious problems. Read More