Water’s where skeeters are

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osquitoes are a nuisance. They buzz. They bite, and they can be a health hazard. Once they have descended on a back yard, removing them might be harder than anticipated, says Joanne Hutton, a horticultural technician for Arlington County.

Homeowners should start by emptying all sources of standing water, she says. Cleaning the roof gutter also is a good idea.

“Mosquitoes can breed in as little as a tablespoon full of water,” Mrs. Hutton says. “That means not only birdbaths, but pots, pet dishes, gutters, wading pools, old tires, black drainage pipes, plant trays and puddles of water.”

Any water that sits still for three to five days is at risk of hosting breeding mosquitoes, Mrs. Hutton says. All water should be eliminated from flat roofs. Wheelbarrows and canoes should be turned over. Even children’s toys should be cleaned regularly.

“Food doesn’t attract mosquitoes,” Mrs. Hutton says. “It’s all about water and where they breed.”

Insect repellent can be used to keep mosquitoes from biting people, she says. If DEET products are used, they usually are effective. For children, use a concentration of less than 30 percent. Citronella products, such as candles and spray, usually are 60 to 70 percent effective. However, there is no spray program that can be used in a back yard, she says.

“You can only minimize their reproduction,” Mrs. Hutton says. “It’s much more effective than sprays.”

If a person must have a birdbath or pond, Mosquito Dunks are a biological control that can be used, she says. The small ring releases a naturally occurring bacterium that kills the larvae in the water, keeping the larvae from becoming adults.

“I think people avoid outside activities in the summer because of the Asian tiger mosquito, which is active all day long,” Mrs. Hutton says. “Whereas our native varieties tend to be active at dawn and dusk.”

Aside from being a nuisance, mosquitoes need to be controlled because they can carry the West Nile Virus. Sometimes the virus has no symptoms, or mild flulike symptoms, but in rare cases can cause West Nile meningitis and West Nile encephalitis. Many birds have been affected by West Nile Virus, including bluebirds, chickadees and titmice, she says.

Aside from water, dense ground cover, such as English ivy, can provide a good resting place for mosquitoes, says Jan Serrigan, an extension agent at Arlington County.

“It’s not just breeding habitats, but resting habitats that can lead to lots of mosquitoes in your yard,” Ms. Serrigan says. “If you are having mosquito problems and you have a plant like English ivy providing low, dense ground cover, you might want to look at ripping it up.”

Even the most well-intentioned people can accidentally breed mosquitoes, says David Gaines, an entomologist at the Virginia Department of Health in Richmond. He has a doctorate in entomology.

For instance, potted plants sit on little trays that hold overflow water. The water in those trays is enough to breed mosquitoes, he says.

Once, a homeowner with a large deck couldn’t figure out why there were mosquitoes in the yard, he says. Old ice chests had been stored beneath the deck, and when it rained, the chests filled, creating a breeding ground for the mosquitoes, Mr. Gaines says.

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