Garden dectective: Gnats

Published: Saturday, Feb. 9, 2013 - 12:00 am | Page 7CALIFORNIA LIFE

As you know, last year was one of the worst for gnats in the Sacramento area. It was reported in the media, including the Sacramento Bee, but I have not seen anything on what to do to eradicate them.

Our backyard was especially overrun, as were we and our dog when we went into the yard. They also got all over our plants and citrus trees. We don't want to "just wait them out" any longer. I have tried a couple of liquid insecticides, but no help. What can I get to spray our grass, plants and trees to end these pesky gnats? – Eddie Henry, Sacramento

According to UC master gardener Carol Rogala, the tiny flying insects that many people call "gnats" are fungus gnats. They thrive under moist conditions, especially where there is an abundance of decaying vegetation and fungi.

These bugs like it moist. Avoid overwatering and provide good drainage. Allow the surface of container soil to dry between waterings. Clean up free-standing water and eliminate plumbing or irrigation system leaks.

Moist and decomposing grass clippings, compost, organic fertilizers and mulches are favorite breeding spots. Minimize organic debris around buildings and crops where larvae feed.

Avoid fertilizing with excessive amounts of manure, blood meal or similar organic materials.

Predators, such as rove beetles (of the family Staphylinidae) and ground beetles (from the Carabidae family), help control fly larvae outdoors in areas not sprayed with broad- spectrum insecticides.

Insecticides are rarely, if ever, warranted to control these flies around homes. However, if insecticides are required for fungus gnats, consider using Bacillus thuringiensis subsp. israelensis or Steinernema feltiae nematodes to control the larvae in plant containers.

Pesticides are poisonous. Always read and carefully follow all precautions and safety recommendations given on the container label.

Store all chemicals in the original labeled containers in a locked cabinet or shed, away from food or feeds, and out of the reach of children, unauthorized persons, pets and livestock.

A complete description of this pest's identification, life cycle, damage and management can be found online at


Questions are answered by master gardeners at the UC Cooperative Extension services in Sacramento and Placer counties.

Send questions to Garden Detective, P.O. Box 15779, Sacramento, CA 95852. Send email to h& Please put "Garden Detective" in the subject field and include your postal address. To contact your UC Extension directly, call:

• Sacramento: (916) 875-6913; 9 a.m.-noon and 1-4 p.m. weekdays

• Amador: (209) 223-6838; 10 a.m.-noon Monday through Thursday; email

• Butte: (530) 538-7201; 8 a.m.-noon and 1-5 p.m. weekdays

• El Dorado: (530) 621-5512; 9 a.m.-noon weekdays

• Placer: (530) 889-7388; 9 a.m.-noon on Tuesdays, Wednesday and Thursdays or leave a message and calls will be returned

• Nevada: (530) 273-0919; 9 a.m.-noon Tuesdays through Thursday or leave a message

• Shasta, Tehama, Trinity: (530) 225-4605

• Solano: (707) 784-1322; leave a message and calls will be returned

• Sutter, Yuba: (530) 822-7515; 9 a.m.-noon Mondays and Tuesdays and 1-4 p.m. Thursdays

• Yolo: (530) 666-8737; 9-11 a.m. Tuesdays and Fridays, or leave a message and calls will be returned

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