Fungus gnats are small mosquito-like insects measuring between 1/8 to 1/10 inches long. The maggots a thread-like, legless, and have black heads and transparent bodies. Eggs hatch and develop into adult gnats in about four weeks.
Fungus gnats are a common household pest found most often in potted plants and flower boxes. They can become a nuisance when large numbers hatch at once and they begin to infest other plants in the house. The gnats thrive in the moist hummus rich soil ideal for houseplants. The maggots live in the soil, feeding on the decomposing plant matter as well as plant tissue. They often cause root damage which leaves the plant stressed and prone to disease.
Adult gnats often lay eggs in indoor plants placed outdoors for the spring and summer seasons. Be sure to inspect all plants before they are brought back indoors. Any plant showing signs of heavy infestation should be disposed of. Keep all plants free of leaf litter which will attract the gnats. Remove damaged plant material as soon as possible.
First signs of an infestation may be wilting and yellowing in the plants. There may be poor growth and foliage loss. Fungus gnats pose no threat to humans or animals. Infestations are easiest controlled when discovered early and the effected plant(s) are isolated. Monitoring can be accomplished using yellow sticky type boards or traps that can be placed discretely among the plants and checked for trapped adult gnats.
To control the fungus gnats once they have been discovered, apply Bacillus Thuringiensis Berliner var. israelensis to the soil to kill the maggots. This can be found at garden centers or through online retailers. The adults can be easily killed with a pyrethrin bases spray or any pesticide aerosol labeled “flying insects”, also readily available at garden centers..
The best long term control of fungus gnats is to prevent their introduction to begin with. Buy your plants from a reputable greenhouse that has a well established pest control policy. Choose only healthy looking plants showing no signs of stress or damage.
Keep new plants isolated for a period of time to ensure no infestation that may spread to your other plants. Utilize your yellow sticky traps to monitor the new plants before introduction to flower boxes or potted collections. Over watering can also lead to an infestation. Proper watering will minimize ideal gnat growth. Allow the soil to dry between watering.
Practice good sanitation. Do not use outdoor compost for indoor plants unless you are absolutely curtain it composted at a high enough temperature to kill pests. Eggs will hatch in four to seven days, so isolate any new soil for a week and check with sticky traps for signs of adult gnats. Soil not found having gnats is now safe to use in your potted plants.
Soil moisture monitoring devices are available that can help insure you are not over watering and creating an ideal breeding ground for fungus gnats. An added benefit of a moisture monitoring device is your plants will always be getting just the right amount of water which will lead to overall healthier plants.
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