I have had a problem for several years with fungus gnats in my houseplants. I went to a florist and bought systemic insecticide, which killed the insects but I am concerned about the strong smell and safety of my cat and dog. The insects returned and I tried insecticidal soap that damaged my plants and did not control the gnats. Is there something more NATURAL that I can use to get rid of them? The bugs eventually kill the roots and are eating the leaves.
Fungus gnats feed on the decaying roots and organic matter in the soil making them a nuisance usually not a detriment to the overall health of your plant. Keeping the soil slightly dry is often enough to discourage these pests. Or you use a yellow sticky trap to capture these pests. Lay the yellow trap horizontally on the potting mix surface or flat on the container rim to capture the adults. Quartered potatoes can be placed on the potting mix to attract and capture the larvae. Or you may want to try Bacillus thuringiensis israelensis (Bti). This bacteria kills the larvae of fungus gnats and mosquitoes but won't harm other insects, pets or people. It is sold under several trade names including Gnatrol and Knock-Out Gnats.
The root damage you are observing may be a result of the insecticide. When applied to dry soil or sensitive plants it can damage the roots. Always read and follow the label directions when using any product natural or traditional products. The label provides guidelines for safe application and lists plants that may be sensitive to the product. If root decay continues you may want to adjust your watering or make sure something else is not feeding on the roots and leaves of your plants.
Photo: Susan Ellis