by Jes-c French, Somervell County Master Gardener Intern
Even in our relatively warm climate here in Somervell County, I’m sure there are many who brought some plants indoors to help them survive the cold of winter. I did, and with them some unwanted pests: fungus gnats.
I was asking for trouble from the moment I moved the plants indoors, because I didn’t adjust my watering appropriately. When plants are outside, they require more water because of the strong sunlight, heat and wind evaporation. Once they are brought inside, less water is needed because of lower light, temperature and wind (Browning). I had a routine to watering my plants, and when I brought them inside I continued on with the routine for a while before realizing I was overwatering.
When I understood my watering errors, I cut back on the frequency, hoping that the larvae would die off if they didn’t have a nice, wet environment to thrive. I also used yellow sticky traps to trap the adult gnats, keeping them from laying more eggs in the soil. Placing the sticky traps horizontally on top of the soil, beneath the foliage seemed to be the most effective way to trap the adults.
Fortunately, this method effectively solved my minor gnat problem. In some cases it might not be enough though. If there are still gnats flying around, you haven’t gotten to the root of the problem. Since the adults have short lives, one can assume there are still larvae in my soil (Savonen, 2006).
One way to address the gnats when simply letting the soil dry out doesn’t work is to completely repot the plants. The plants should be rinsed, the pots disinfected, and fresh soil that isn’t infested should be used. The infested soil can be solarized to kill the larvae. There are, however, other options if you do not want to repot your plants.
Adjusting our watering practices is a great first step of integrated pest management, but there are also chemical treatments that can be incorporated in the overall strategy. One highly recommended microbial insecticide for the larvae is Bacillus thuringiensis. Alternatively, parasitic nematodes, predatory mites, insect growth regulators, such as azadirachtin, or nerve-active insecticides, such as chlorphyrifos, can be used to kill the larvae (Drees, 1994).
For several other insecticide recommendations for killing both larvae and adult fungus gnats, see Drees’ Fungus Gnat Management at http://extentopubs.tamu.edu/bulletins/uc/uc-028.html.
Browning, Sarah. “Winter Care of Indoor Plants (winter_houseplants).”Winter Care of Indoor Plants
(winter_houseplants). UNL Extension, n.d. Web. 25 Feb. 2016.
Drees, Bastiaan M. “FUNGUS GNAT MANAGEMENT.” FUNGUS GNAT MANAGEMENT. Texas A&M
University System, 1994. Web. 25 Feb. 2016.
Savonen, Carol. “Do Your Potted Plants Have Fungus Gnats?” Do Your Potted Plants Have Fungus Gnats?
Oregon State University Extension, 29 Dec. 2006. Web. 25 Feb. 2016.