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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Like this comment
Posted by Alix
a resident of Triple El
on Feb 13, 2018 at 3:04 pm

I do not appreciate being notified 2 days before spraying near my home. I also don’t appreciate that the notification came to me only via Palo Alto online. Postcards should be mailed to homes at least 2 weeks in advance. Further I find it obnoxious and condescending that the chemical names were not disclosed in the article. I visited Santa Clara Vector Control site & called them. The chemicals contain methoprene & bacillus thuringiensis. The former is used for mosquitoes that could carry West Nile virus. The latter is used to make Bt corn - genetically modified corn. The only human feeding study of Bt corn was halted early when the Bt DNA was found to be incorporated into the DNA of our biome, making humans into pesticide factories. Is it safe outside of use in Bt crops? I don’t know. Supposedly its used in organic gardening. The other chemical, methoprene, is an endocrine disruptor which very likely does the same in humans. We are exposed to an awful lot of endocrine disruptors. I can assume at best this is additive to our other exposures.

The final reason I’m angry about the spraying is that the article just says mosquitoes are annoying. For an annoyance, the cost benefit equation does not work. I would like the City of Palo Alto to find another way to control mosquitoes in the future, if they need to be controlled. As a city we operate on green principles. This spraying is not in line with that ethic.

1 person likes this
Posted by Anon
a resident of Another Palo Alto neighborhood
on Feb 13, 2018 at 4:23 pm

I'm unsure what I the object of the spraying for the Winter Salt Marsh Mosquito (Aedes squamiger) might be.

Here is a Napa county web link:

Web Link

West Nile is generally transmitted via Culex species, e.g.:

Culex pipiens pipiens
Culex pipiens quinquefasciatus

Sorry, but further commenting on this topic has been closed.

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