Annual mosquito treatment at baylands starts Wednesday

Vector Control District will distribute larvicide to keep out mosquitoes

Santa Clara County will begin its annual treatment Wednesday of the Palo Alto Baylands to prevent the spread of the winter salt marsh mosquito, which lays eggs in moist soil, like the kind found at the popular hiking and biking destination.

The Santa Clara County Vector Control District announced that the marshes will be treated with naturally occurring soil bacteria and "a mosquito-specific hormone" that is not harmful to the surrounding environment, wildlife or humans. The soil bacteria produces an insecticidal protein when consumed by the mosquito larvae, effectively killing them. The eggs can lay dormant for many years, even with repetitive flooding, according the district.

For some of the less accessible marsh areas, including the Palo Alto Flood Basin, a helicopter will be used to "cover large areas and minimize impact to the marsh habitat," the district said. The helicopter crew may fly at low altitudes over the treatment area within the basin.

The treatment, scheduled to begin in Palo Alto at 7:30 a.m., covers an area roughly bordered by Adobe Creek to the north, Adobe Creek Loop Trail to the east, East Bayshore Road to the south and Mayfield Slough to the west.

A helicopter will also be used to treat Zanker Marsh in San Jose; the total area to be treated is close to 1.5 square miles, according to the district.

"The plan was to (treat the land) this or next week, because the weather is helping the mosquitos to grow faster," district manager Nayer Zahiri said. "When the adults hatch, they're so aggressive that if we don't treat it, they will be a problem."

The winter salt marsh mosquito is known for being active during the day, and is able to fly over 15 miles from its breeding grounds to feed on humans and other mammals, the district said in a press release. Current conditions, including the recent warm weather, "indicate a high probability that a significant number of salt marsh mosquitoes" could become adults as soon as early to mid-March if the area is left untreated.

Zahiri said there was no precaution issued for residents because the treatment is "very specific to mosquito larvae," and not harmful to humans or pets. The county has been using this treatment method each year since 1992. She also noted that that in the past, the treatment of the marshes has resulted in a 90 percent reduction in the mosquito population, and minimizes the irritation they can cause.

Residents are advised to avoid any areas where the helicopter is operating and encouraged to take preventative measures, such as dumping out standing water, wearing long shirts and pants and applying repellent when outdoors to reduce the chance of getting mosquito bites.

To report mosquito-breeding grounds, contact the district by calling 408-918-4770 or filing a request online at

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4 people like this
Posted by John
a resident of Monta Loma
on Feb 14, 2018 at 11:47 pm

Once the mosquitoes are "treated" to some naturally occurring poisons, consideration should be given to "treating" Google to reduce overcrowding. The Mountain View City Council will not stop the spread of Google. It will eventually suck the life blood out of the city. In a decade, Mountain View could be renamed El Goog.

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