Stymied by evening winds for the past week, an effort to kill the disease-carrying mosquitoes by aerial pesticide spraying in southern Sacramento County is going back to square one.
The Sacramento-Yolo Mosquito and Vector Control District scheduled and canceled spraying again on Thursday night.
David Brown, general manager of the agency, said the district hopes to treat the region for three consecutive nights as soon as the weather allows.
On Aug. 11, the agency began what were supposed to be three straight nights of aerial treatments over 66,000 acres of the county south of the American River.
But the contractor hired to do the spraying had to stop about halfway through the job because of wind. Brown has said aerial treatments cannot be done in winds of more than 8 mph.
"I don't want to say that it didn't do anything," Brown said Thursday of that aborted effort last week. "(But) just that one time wasn't enough to significantly reduce the mosquito population."
Brown said his goal is to knock down the population by 70 percent. A single night's complete application is estimated to kill about 35 percent.
The district took the step last month of ordering aerial spraying in an attempt to stem the spread of West Nile virus, which is transmitted by the bite of infected mosquitoes.
On Aug. 8-10, about 50,000 acres of northern Sacramento County were sprayed by airplanes. The district is using the pesticide EverGreen Crop Protection EC 60-6, which is a mixture of piperonyl butoxide and pyrethrins.
On Thursday, the mosquito agency also announced that the rate of infected mosquitoes in Yolo County had risen to the point that ground spraying will begin sometime next week in Davis and Woodland.
Brown said monitoring has found slightly fewer than five infected mosquitoes per 1,000 in Woodland, four per 1,000 in Davis and five per 1,000 in the small town of Madison. Five in 1,000 is considered epidemic level. Sacramento County had infection rates as high as 23 infected mosquitoes per 1,000 in some places in late July.
Aerial spraying over agricultural areas of Yolo County, which has been going on all summer, will continue as well.
Brown said the decision to spray Davis and Woodland from trucks rather than by airplane was based upon the geographical size of those cities, not political sensibilities.
Pointing to a map on the wall of his office, Brown said Davis and Woodland cover roughly 4,000 to 5,000 acres apiece - comparable in size to the Pocket neighborhood in Sacramento County, which was treated with truck-mounted sprayers this week.
At last count, Sacramento had 47 confirmed cases of the disease, the highest of any county in California, which has logged a total of 208 cases. Six people in the state have died.
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- The Bee's Edie Lau can be reached at (916) 321-1098 or firstname.lastname@example.org. Bee staff writer Deb Kollars contributed to this report.