How to Get Rid of Gnats on Vegetable Seedlings
Fungus gnats are any number of insects from the order Diptera. These tiny winged creatures are a colossal headache for commercial greenhouse keepers as well as home gardeners who start vegetable seedlings indoors or in cold frames and hoop houses. The insects thrive in compost and decaying plant matter, and cause damage to seedling roots and growth. Fungus gnats can be difficult to control, but precautions and persistence can rid your vegetable seedlings of gnats. Does this Spark an idea?
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Things You'll Need
- Unscented chlorine bleach
- Fresh potting soil
- Aged compost
- Lemon oil or orange oil
- Insecticidal soap
- Bacillus Thuringiensis var. israelensis (brand name Knock-Out Gnats) OR bT-i mosquito control flotation discs
- Fine peat moss
- Diazanon or Nicotine based insecticidal foggers OR Pyrethrin based insecticidal spray
Instructions
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Prevent fungus gnats from getting started on your vegetable seedlings by using clean seed-starting practices in your greenhouse or home garden seed trays. Wash seed-starting pots, trays, and benches thoroughly with a mild bleach solution before each growing season. Use fresh potting soil and well-aged compost, as components in compost less than six months old may encourage fungus gnat populations. Keep the seedling area clear of all decaying plant matter.
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Monitor growing seedlings carefully for signs of fungus gnat infestation. Exercise caution when watering. Do not over-water, and ensure that seedling trays have good drainage as well as adequate air circulation. Add a bacillus Thuringiensis var. israelensis (bT-i) mosquito-control disc to watering cans for home gardening seedling trays, or use a liquid bT-i soil drench in watering vegetable seedlings in larger scale greenhouse operations, as bT-i helps kills fungus gnat larvae as they emerge from the soil. Check labels and instructions carefully in using these products; be sure to select a bT-i product approved for use on vegetables intended for human consumption.
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Increase the concentration of bT-i in watering at the first sign of flying gnats; this will help prevent the next generation of larvae from getting established in the soil. Spray the vegetable seedlings with insecticidal soap mixed with water according to manufacturer's directions. Wipe the edges of the pots, trays, and shelves down with lemon or orange oil.
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Rub peat moss through a metal screen until it is fine and powdery. Spread this on the surface of all vegetable seedling trays to deter fungus flies from laying eggs in the soil. Rub a few drops of lemon or orange oil into the fine peat moss to increase its deterrent power.
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Use pyrethrin-based household insecticidal sprays for persistent fungus gnat infestations in home or small-scale vegetable seedling areas. Commercial greenhouse vegetable growers may opt for diazanon or nicotine based insecticidal foggers. Follow manufacturer's label instructions carefully for safe use of these insecticidal products to get rid of fungus gnats on your vegetable seedlings.
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Tips & Warnings
Electronic bug zappers can kill significant numbers of fungus gnats at night in greenhouses, though the noise may be too inconvenient for indoor use in home gardening operations.
Prevention is always easier than eradication of fungus gnats; when facing a severe infestation, consider jettisoning your present crop of vegetable seedlings and starting over with a fresh batch.
