Questions on Plant Care and Gnats

Who likes insects in your house? It is annoying to have gnats swarm around you when you water or move your houseplants. These flying pests, known as fungus gnats, can be easily controlled with the right knowledge and care routine. Cultural practices used in conjunction with biological controls are the best way to rid your houseplants of gnats permanently.

What are Fungus Gnats?

The name, fungus gnats, can apply to several species of insects. They are members of the order Diptera, family Sciaridae. The four most common species found in indoor plants are the dark winged fungus gnats Bradysia, paupera, impatiens and coprophila.

How do I Identify These Pests?

Adult fungus gnats are 1/8 inch long and gray to black in color. They are delicate looking, with thread-like antennae and long, slender legs. Fungus gnat larvae are clear to cream colored, and can be up to 1/4 inch in length with shiny black heads.

What Damage Do Fungus Gnats Cause?

The larvae of fungus gnats can damage plant roots, causing stunted growth, discolored foliage, and even the death of young plants.

How Do I Control Gnats in my Potted Plants?

Over-watering is the major cause of fungus gnat infections. Fungus gnats thrive in wet soil, so the best preventive cultural control is to let the soil dry completely between waterings. Yellow sticky cards can be placed on the potting medium to capture the adults, or they may be sprayed with insecticide, but this is not an effective control method when used alone. To control fungus gnats, you must control the larvae. Bacillus thuringiensis israelensis (BTI) is an effective soil drench. This is not the same BT that is used for garden caterpillar control, but is specifically effective against flies in the Diptera family. BTI is only effective for 48 hours, so up to three applications may be necessary. Do not mix BTI with fertilizers or fungicides. BTI does not affect adult gnats. Hypoaspsis miles, a predatory mite, is also effective against fungus gnat larvae. The mite persists in the soil for long periods, often feeding on the remains of dead maggots. This mite also will control thrip pupae and other insect larvae.

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About this Author

Maddie Gardener is a freelance writer who enjoys sharing knowledge with others. She has been writing online for two years with various sites and private customers. She has degrees in business management and horticulture, and over 20 years experience in the horticulture field.

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