How to eradicate fungus gnats from house plants for good?
Laramie County Wyoming
If you have you houseplants planted in mixes with lots of organic matter and they are species that can't withstand frequent (at least weekly) drying down to point that it interrupts the fungus gnat life cycle you have to resort to other measures to control them. I gave away or replaced house plants in the break room at work that couldn't survive on a single light watering once a week and reduced the fungus gnats almost completely. If you don't want to do that you can repot the plants into soil mixture with more mineral content and lot less organic matter. The fugal decay in potting mixes with lots of peat moss is great habitat for fungus gnats. I don't know if you can achieve your goal of total eradication of the fugus gnats "for good" but you certainly reduce them. There are now also systemic insecticides and insect parasitic nematodes labeled for fungus gnats in house plant pots. For a more complete information please read this excellent bulletin from Profs. Cranshaw and Cloyd: https://extension.colostate.edu/topic-areas/insects/fungus-gnats-as-houseplant-and-indoor-pests-5-58... Please let me know if you have any additional questions.