Workers from the Baker Valley Vector Control District sprayed a mosquito-killing fog in parts of Baker City Monday night, and district manager Matt Hutchinson said the plan is to cover the rest of the city tonight and Wednesday night.
On Monday night the district's two fogging trucks covered areas north of Campbell Street and east of 10th Street, Hutchinson said.
Tonight the crew hope to cover areas east of the railroad tracks and south of Campbell to about the railroad tracks, and to fog the rest of town Wednesday night.
Hutchinson said the fogging trucks won't start rolling until after 9 p.m.
With thunderstorms in the area, Hutchinson said a light rain wouldn't cause a problem but heavy rain, and wind, could force crews to postpone their work.
Mosquitoes aren't as active when the ground is very wet or when the wind is strong.
"We want to get out when the mosquitoes are most active," Hutchinson said.
He said residents needn't take any special precautions, although he said fogging trucks usually stop spraying while passing homes with obviously open windows.
They also cease fogging when they drive past pedestrians.
Hutchinson said the pesticide the district uses, called permethrin, is approved for mosquito control by the U.S. Environmental Protection Agency.
The liquid that's sprayed contains 8 percent active ingredient, he said.
Under ideal circumstances the permethrin fog can kill mosquitoes up to 300 feet from the fogger, Hutchinson said.
The EPA first approved permethrin for use on cotton fields in 1979. From 1982 to 1989 the agency allowed the pesticide to be sprayed on a variety of other crops, including fruits and vegetables.
The EPA said permethrin is highly toxic to fish and aquatic invertebrates, and to bees, and is classified as a restricted use pesticide.
There are formulations containing permethrin that are available for household use, as well.
In 2003 the EPA approved the sale of clothing impregnated with permethrin; the garments are supposed to repel mosquitoes and other insects.
Permethrin also is an ingredient in many products designed to protect pets from fleas and ticks.
According to the National Coalition Against the Misuse of Pesticides, for humans permethrin has a "fairly low acute toxicity, producing symptoms mainly of irritation."
The organization has urged EPA to monitor the potential cumulative effects of permethrin, however.