Pima County Cooperative Extension

Pima County Home Horticulture


Arizona Daily Star
Gardening Column for August 18, 2002


The outbreak of West Nile virus that has caused such concern in Louisiana is making it's way west. Cases of the virus have already been reported in Texas, and health officials estimate that the virus could make it's way to Arizona as soon as November of this year.

The virus is carried by mosquitos, and although the desert environment doesn't provide the most fertile breeding grounds, standing water of any size can breed mosquitos! That's why it's important to eliminate all possible breeding areas around the home.

Even small spots where water collects can provide a location for hundreds of mosquito larvae to develop. Mosquitoes can develop in any standing water lasting more that seven to ten days. Uncovered trash containers, cans, plastic containers, flower pots, and old tires can all hold water for considerable lengths of time. If tires are used as children's swings, then drill holes in the bottom to keep water from collecting. Check hidden locations as well. Containers may be lying concealed in overgrown vegetation or behind walls and fencing.

Remove drainage saucers from pots sitting on the patio. Place these pots on "pot feet" to allow the water to drain out and away from the pot. Wheel barrows and garden carts stored in the yard should be turned over to prevent water from collecting. Remove water that collects in depressions in tarps covering boats and other equipment or objects.

Some spots where mosquitos breed are not so obvious. Bird baths for instance, can harbor mosquitos if the water is not changed on a weekly basis. Swimming pools should be maintained with the proper levels of chlorine. The water in children's wading pools should be changed weekly. Fountains should be kept running. If fountains are turned off, empty out the water.

Water gardens are popular, but they are a major mosquito source if the water stagnates. Provide aeration for these ornamental pools or stock them with mosquito eating fish.

Rain barrels and other water harvesting containers must be sealed tightly to keep mosquitos out! If rainwater storage containers are not sealed, place a "mosquito dunk" in the barrel or container. Mosquito dunks are actually a special formulation of the often used garden spray BT (Bacillus thuringiensis), designed to control the mosquito's larval stage.

Bacillus thuringiensis israelensis or Bti, is a naturally occurring soil bacterium that is perfectly safe to birds and mammals. Besides rain barrels, Bti mosquito dunks can be placed in bird baths, fountains, water gardens and ponds to prevent mosquito development. They provide 30 days of protection before needing replacement. Dunks are available at most garden center and hardware stores.

Gardeners and others venturing outside should consider applying protective sprays of mosquito repellent. Choose a repellent containing DEET. Mosquitos are attracted to animal skin odors and the carbon dioxide from their breath. When a mosquito gets close to a host, DEET jams the insect's sensors and confuses it so it is unable to find the host and land.

Read and follow instructions on the label to avoid excessive use and over-application. In most cases products with 25 to 35 percent DEET provide adequate protection for adults. Lower concentrations are used for children. Do not allow children to apply DEET repellent themselves, and do not use DEET on infants.

DEET products usually repel mosquitoes for several hours. However, repellents are effective only at short distances from the treated surface, so you may still see mosquitoes nearby. As long as you are not being bitten, there is no need to apply more repellant.

In conjunction with mosquito repellent, wear appropriate clothing. Shoes and shocks, and long-sleeved pants and shirts minimize exposed skin. Pant legs can be tucked into shoes or socks, and collars buttoned for further protection.

Finally, avoid the "gimmick" devices advertised to control mosquitos. Electric bug zappers and high frequency sound repellers neither control or repel mosquitoes. Outdoor chemical foggers may keep mosquitoes away for a few hours, but once the chemical dissipates, the mosquitoes will return. If the air is calm, citronella candles can be used to keep mosquitoes away from patios, porches and other outdoor activity areas.

       BACK to the West Nile Virus information page

       HOME to the Master Gardener's home page.


Materials last updated on September 9, 2002
Located at http://ag.arizona.edu/pima/gardening/
Pima County Master Gardener Webmaster (Website-related Questions and Comments): Linda G. Drew
(c) 2001 The University of Arizona. All contents copyrighted. All rights reserved.