Dr. Wally

How to Knock a Fungus Gnat Flat
Did you have your houseplants outside this summer?
Did you bring any new plants home?
Did you re-pot any plants recently?

Symptoms: Small, black flies (resembling fruit flies) seem to suddenly appear out of nowhere, slowly buzzing around areas near your houseplants, and often in your washrooms. Their larvae, little worms about 1/8 of an inch long resembling grubs with white bodies and black heads, are often seen moving in your plant’s potting soil near the stems.
Diagnosis: Fungus Gnats

Prevention
There are a number of things you can do to prevent an infestation of fungus gnats. First, buy your houseplants from a reliable source. Chain stores and grocery stores often do not treat plants with insect problems. You “inherit“ the problem as soon as you bring the plant home. Second, avoid poor quality potting soil or soil left open outside. When fungus gnats appear after repotting you should be suspicious of the potting soil you just used. The soil may have a familiar brand name, but that doesn’t necessarily mean it’s free of insect larvae. Invest in quality potting soil, preferably a soilless mix, and you’ll avoid these annoying pests in your home! Third, two weeks before you bring your houseplants in for the fall, use one of the treatments in the second half of this article as a preventative.

Control
If you find that one of your plants is infested, you can work to control the damage. Isolate the infected plant in another room. Then, let the top 1/3 of the plant's soil dry before rewatering. This will limit larvae that depend on damp conditions. And make sure to empty the plant’s saucer after watering.

Spraying these gnats in flight with pesticide is not practical and should be avoided for safety purposes. However, trapping the gnats is safe and effective. Set up some yellow sticky traps around your plants. Sticky traps are available commercially or you can make your own. Paint a 12-ounce can a bright, high gloss yellow. After the paint is thoroughly dry, coat the can lightly with Vaseline petroleum jelly. Place or hang the sticky trap cans near your houseplants or in any area in the house where you have seen the insects. (Fungus gnats are drawn to lights.) To re-use these traps, simply wipe accumulated gnats off the cans and reapply the Vaseline. These traps also work well as a whitefly monitor.

You can set out a bowl of water mixed with scented bath soap. This will also act as a trap, and gnats will drown in the solution. If gnats appear in your bathroom, spray bleach or bathroom cleaner into sink and bathtub drains and overflows to eliminate larvae and adults. Plug up or tape the openings for a day or two to prevent escape.

Treatment--Organic
Repotting may be helpful but some larvae may be entwined in the clump of soil around the roots. Be careful not to remove soil from the roots.,Tthis may injure the plant! Use fresh potting soil and clean the container with 1 part bleach to 8 parts hot water to eliminate any insect eggs. After re-potting, water the plant. When the surface soil is dry, liberally apply diatomaceous earth across the top of the soil (reapply after watering). Seal the top of the container with Saran wrap .The gnats and larvae will get cut up and dehydrate after contact with the diatomaceous earth. (Diatomaceouse earth is finely milled fossil shells of prehistoric single celled freshwater plants called "diatoms.") Continue this treatment for 2 weeks till all remaining gnat eggs are hatched out.

You can dispose of the larvae using the bacteria bacillus thuringienisiIsraelensis. Pour ½ packet of Mosquito Beater granules (if you’re using Mosquito Dunks use ¼ of the wafer) into a gallon of warm water and shake well. In a day, the granules should be dissolved and the water will be back to room temperature. Shake up the mixture and drench the infected plants soil. Water the plant as you would routinely do with this mixture for 1 week.

Fungus gnats can also be effectively controlled by doing a soil drench using beneficial parasitic nematodes (species Steinernema feltiae). Beneficial nematodes are microscopic roundworms that enter fungus gnat larvae through natural openings such as the mouth, anus and breathing pores. The nematodes give off bacteria that digest the entrails of the larvae. Fungus gnat larvae die within three to four days.

Treatment--Conventional
Treat the soil with Bonide’s Systemic Granules per instructions.
Spray the infected plant with Bonide’s Eight Garden & Home R.T.U. (Permethrin 0.02%) per instructions.

Before using pesticides read and understand all directions and precautions on the label. If you have any questions, contact the place of purchase or the manufacturer. Even though a curative is listed as organic or natural, directions and precautions still must be adhered to. Carefully read a label’s list of ingredients. A case point is two pesticides with similar spelling and pronunciation. Permethrin is a synthetic chemical found in a variety of products listed for home and garden use. Depending on the concentration, Permethrin can have a residual of up to four weeks. Pyrethrin is an organic- botanical pesticide made from extracts of pyrethrum daisies. Pyrethrin kills on contact and has no residuals. NOTE: Both pesticides have precautionary warnings on their labels.

 

Don’t Panic – Go Organic!

Wally Schmidtke
Pesches Garden Center Manager
www.pesches.com

 

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