My Spider Plant Is Full of Gnats

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Fertilize your spider plant once a month with a complete fertilizer to help restore its health from fungus gnat damage.

Spider plants, or Chlorophytum comosums, are popular indoor and outdoor adornments. The plants thrive in temperatures between 60 and 80 degrees Fahrenheit, according to Colorado State University. Unfortunately, spider plants — even when grown in the best conditions — can become infested with small insects called fungus gnats. Fungus gnats cause damage to spider plants' root systems if left untreated.


Fungus Gnats

Fungus gnats are small, black-bodied insects that are often confused for mosquitoes. Adult fungus gnats do not cause problems for spider plants; however, their larvae feed off roots. These pests lay their eggs within the first 3 inches of potting soil. When eggs hatch, fungus gnat larvae feed off roots for two to three weeks before maturing into adults. Gardeners may see their fungus gnat population skyrocket due to the fact that female gnats lay up to 200 eggs per a lifetime.



Spider plants experiencing a fungal gnat infestation display stunted growth. Larvae eat away at root systems, which prevents the plant from growing. Other symptoms of fungus gnats include yellowing leaves, nutritional problems, wilting and defoliation. Damage caused to the root systems creates the perfect entryway for other diseases such as pythium, botrytis, verticillium and fusarium. Furthermore, spider plant cuttings cannot develop root systems when fungus gnat larvae are in the soil. Employing both cultural and chemical treatments for spider plants keeps them from declining in overall health.


Cultural Treatment

Repot your spider plant to treat your fungus gnat problem. Use a peat-based potting medium that has loam soil to keep your plants from falling over. Also, alter your spider plant's watering routine to kill off fungus gnats. Avoid overwatering your spider plants. Between waterings, press your fingers into the first 3 inches of potting soil to make sure that it is dry. Allowing the surface of the soil to dry out makes your spider plant a less attractive breeding site for fungus gnats.


Chemical Treatment

Treat your spider plant with a microbial insecticide soil drench called bacillus thuringiensissubsp. israelensis. Bacillus thuringiensissubsp. israelensis produces toxins that kill off fungus gnat larvae. In addition, gardeners may apply granular insecticide that contains imidacloprid to kill larvae. Adult fungus gnats are killed with insecticides that contain bifenthrin, cyfluthrin or permethrin. Apply the insecticide to the surface of the soil, so that adults are killed when they emerge. When applying any type of insecticide, keep spider plants away from pets and children.