The fogging in Santa Clara County will target parts of Mountain View and Los Altos where there has been an increase in mosquito activity and West Nile virus was found in some adult mosquitoes, Santa Clara County Vector Control District spokesman Bob Kaufman said.
The fogging will begin around 11 p.m. and last for about four hours in an area roughly bordered by Villa Street and Escuela Avenue on the north; Clark Avenue, Verano Drive, North Gordon Way, South El Monte Avenue and Campbell Avenue on the west; state Highway 85 and Sun Mor Avenue on the east; and Covington Road and Levin Avenue on the south.
Kaufman said the substance sprayed is only toxic to mosquitoes and is sprayed at less than an ounce per acre.
About a quarter of the area being targeted tonight was previously fogged during an operation on Aug. 9, Kaufman said.
He said that said after a fogging, adult mosquito populations usually decrease by about 80 percent, which, in turn, helps decrease the odds of West Nile virus spreading to humans.
"If there's less mosquitoes flying around ... that's going to reduce the chances," Kaufman said.
He said the vector control district keeps a close eye on larvae sites and monitors buckled curbs and streets where water can pool and provide a mosquito breeding ground.
Residents are asked to drain any standing water around their homes, and properly maintain their swimming pools.
Kaufman said that although West Nile virus activity is on the rise nationwide this year, Santa Clara County appears to be seeing only average activity.
Last year, the district conducted four sprayings. Tonight's fogging will be the second of the year.
In Contra Costa County, an area in Knightsen off of Holland Tract Road will be fogged after a high number of mosquitoes -- some testing positive for West Nile virus -- were found nearby, Contra Costa County Mosquito and Vector Control District officials said.
The fogging will begin sometime after 7:30 p.m. and continue until about 11 p.m. The area will be sprayed by a slow-moving truck at a rate of 1.5 ounces of insecticide per acre.
District officials said the ultra-low concentration sprayings do not pose safety hazards for residents or the environment.
