Q:Β We have an infestation of fungus gnats inside our house. We have had our bug service spray the plants, the windows, everything twice. They have put granular insecticides in each plant soil twice,and even tried mosquito crystals. Then we had the two rooms containing the plants bombed. Our exterminator used PT Pro-Control Formula 2 (one can in each room). We completely sealed off the rest of the house. Two days later they were back, about 40 percent of what they were. We have a fluorescent light that has a sticky back that we were filling up nearly daily; now it takes about two days to fill. But we still have the gnats. Do you have any suggestions on how to get rid of these persistent bugs?
A:Β Fungus gnats are often found in places that are moist, have decaying plant matter, and, of course, fungus. The larvae of these flies feed on the fungus so that is where the adults lay their eggs. The management method that works best is making the habitat less inviting. With indoor plants this often means less watering to allow the soil to dry out between watering, killing off the fungus. You can also repot and lightly prune plants that seem to have a lot of decaying material and fungus present. There are products that are effective against the gnats but if you continue to provide the fungal habitat, they will be back. Sticky traps are great for monitoring your progress in reducing the population and their habitat.
Peter L. Warren is the urban horticulture agent for the Pima County Cooperative Extension and the University of Arizona. Questions may be emailed to
