Mosquito council agrees to small amount of pesticide use in septics


On behalf of the West Marin Mosquito Council, we want to update readers on our ongoing work with the Marin/Sonoma Mosquito and Vector Control District. The council consists of representatives from West Marin communities, government agencies and nonprofit organizations that have been working with the district to develop and sustain the least toxic approach to controlling mosquitoes in West Marin, which was annexed into the district in 2004. Based on information provided in pre-election materials, many who voted for the annexation believed that the district would only use “environmentally safe” products in West Marin. 

Under the council’s first agreement with the district, signed in 2006, the council educated West Marin communities about mosquito prevention and control, provided information and support for physical prevention methods, assisted with drainage and other standing water issues and—only as a last resort—use naturally occurring bacteria that are effective in controlling mosquito larvae. Today, the council consists of the following representatives: Jim Zell from the Stinson Beach Water District, Grace Godino and Vic Amoroso from the Bolinas Community Public Utility District, Dennis Rodoni from Olema, Sue Kline from Nicasio, Liza Goldblatt from Point Reyes Station, Morgan Patton from the Environmental Action Committee, Paul Reffell from Marshall, Margaret Graham from Tomales, Terry Pebbles, an at-large member and Gordon White from the National Park Service. We also have several affiliate members, such as the Inverness Public Utility District, whom we keep informed. 

A second agreement negotiated in 2007 was extended until this year, and was set to expire in June. Under this agreement, the district was able to use Agnique MMF, an oil that suffocates adult mosquitoes, in septic systems if a significant adult mosquito infestation was found, such as occurs if a septic system is not properly sealed or screened. Unfortunately, that product was recently discontinued, and the district stated that it needed a substitute for it. For the last five months, the council has been meeting with Supervisor Steve Kinsey and district representatives to negotiate a new agreement. Some on the district did not wish to have a separate agreement with West Marin, and in many ways these negotiations were more challenging than previous negotiations. 

Our council supports the least amount of pesticide use in West Marin; however, we felt it was better to have an agreement with the district than not have one at all. In a new agreement, reached this month, we made one major compromise: the district may use a pesticide called methoprene at a very low dilution (2 to 4 parts per billion) in septic systems if it is deemed absolutely necessary. The district also compromised, agreeing to provide important information to both property owners and tenants when they are called to a site, including how to control mosquitoes by fixing septic system problems, a list of local contractors and handypersons who do this work, the contact information for the council and a map of the area covered by the agreement. In addition, the district will provide the council with monthly reports so we can monitor its use of methoprene, as we did with Agnique MMF. 

Of the over 5,000 septic systems in West Marin, the district believes it needs to treat about 100 —with BT, Bs and, when absolutely necessary, methoprene—on a rotating basis. We are heartened that it is using Clarke products, which are California and OMRI-approved, and are looking promising for use in septic systems. 

In the council’s vote on this new agreement, six members supported it, two opposed it and one abstained. The district approved it at their May 13 meeting. A public informational meeting on the new agreement will be held later this summer. The council thanks Supervisor Kinsey for the key role he played in the negotiations. 

We are very fortunate that not one human case of West Nile Virus has been detected in West Marin, and we will continue to carefully monitor this situation with the district. For our agreement to work, it is important for all West Marin residents actively assist in the control of mosquitoes by eliminating potential mosquito habitat. This is why, as mosquito season approaches, ads appear in local newspapers asking you to: screen roof plumbing vents, check seals on septic tanks and be sure your risers are not cracked; walk your property and dump any standing water once a week; check your tarps or old tires for standing water; check dairy waste ponds for mosquito problems; drain watering holes on a regular basis; clean clogged gutters; and manage irrigation water effectively.

If you can screen and seal septic systems and fix the risers, please sign up as soon as possible so we can add you to the list the district will give to septic system owners who are having mosquito problems. Please go to the Environmental Action Committee website,, and fill out the form to be added to the list. 


Grace Godino and Liza Goldblatt are co-chairs, and Margaret Graham is a past co-chair, of the West Marin Mosquito Council.