Biological Control

• Natural biological controls kill gnat larvae without harm to people, pets and wildlife. One pesticide, Bacillus thuringiensis israelensis (Bti), is applied as a soil drench and soaks the soil with bacteria that kills gnat larvae. Another biological control, Steinernema feltiae, mixes beneficial nematodes with water. Applied to the soil, these tiny parasites attack the gnat larvae. It may take two to three weeks for these microscopic pests to significantly reduce the larvae population. These biological controls, available at many garden centers, do not kill the egg-laying adults, but do prevent the larvae from becoming adults.
  
  

Botanical Control

• Plant-based insecticides such as pyrethrins, made from the flowers of chrysanthemums, kill adult gnats and larvae on contact. The botanical ingredient pyrethrum is useful on heavy gnat infestations and is relatively safe for people and pets.These botanical pesticides act quickly for short-term control, but must be reapplied every three to five days when more gnats appear. Because plant-based pesticides may have an unpleasant odor, take the plant or plants outdoors and spray the insects and plant soil, then leave the plant outside for a day to let the insects die and insecticide smell to evaporate.
  
  

Cultural Control

• Reduce fungus gnat habitat by removing dead leaves from the plant soil and allowing the soil surface to dry after each watering. Use sterile potting soil for indoor plants. Outdoor soil or compost often contains gnat eggs that hatch when used for indoor container plants. Remove peat moss used as soil covering because it encourages damp conditions and provides gnat hiding places. Check outdoor plants for fungus gnats crawling on the soil surface. Leave the plants outdoors unless they can be treated for gnat hitchhikers.
  
  

Tips

• Check for fungus gnats by using yellow sticky insect trap cards. Place the traps near the plant to catch adult gnats. When the card has numerous gnats, the plant should be treated. Another detection method is to place a potato slice on the soil. Check under the potato in the early morning for signs of gnat larvae. A decoy plant may help control fungus gnats. Some gardeners fill pots with plant debris and raw compost or sprouting grain. The decoy plants attract female gnats away from other plants. Every two weeks, these gnat-infested pots can be soaked in boiling water or thrown out to get rid of the pests.