County of Marin - News Releases - Invasive Weeds

For Immediate Release
September 08, 2023

Healthy Soils Lens Included in Innovative Weed Management Program

County Agriculture staff participates in three-year pilot

SAN RAFAEL, CA -- A three-year pilot program is underway to eradicate invasive weeds on Marin County farms and ranchlands through sustainable pest management with a focus on healthy soil.

As in so many other places in California, invasive weeds have become an extensive problem for the agricultural lands of Marin County, a verdant ranching and farming landscape just north of San Francisco. Exacerbated by the 2019-2022 drought, thousands of acres of historic pasturelands and rangelands have become unusable as invasive weeds continue to push out desirable plant species and beneficial forage. With fewer acres to graze livestock, these invasive plants are compromising the viability of local ranches and, at the community level, forming dense stands of continuous fuel that increase the risk of catastrophic wildfires.

To address this challenge, the Marin County Department of Agriculture, Weights and Measures and the Marin Agricultural Land Trust (MALT) joined forces to implement the three-year pilot program. The UC Cooperative Extension Marin and Sonoma and the Natural Resources Conservation Service out of Petaluma are also essential partners in the effort.

The voluntary pilot invasive weed cost share program was launched in early 2023 within a segment of the Chileno Valley (Chileno Creek watershed), a 20.25-square-mile area of the county made up of mainly working cattle ranches and dairies that has been significantly impacted by invasive weeds. The primary goal of the initiative is to encourage local ranchers to participate in the development of sustainable pest management plans (SPMs) that consider the environmental, social, and economic costs of invasive species removal. Developing SPMs encourages a holistic, healthy soils-based approach toward pest management and the hope is to establish a new model for eradicating invasive plants that simultaneously supports soil health, water quality, and the biological diversity within this watershed.

Examples of soil health practices include planting cover crops; not-till or reduced till residue and tillage management; prescribed grazing; compost amendment to pasture and rangeland; nutrient management; overseeding to establish desirable plant communities; planting of hedgerows and other shrubs and trees; and riparian restoration.

A secondary goal of the pilot program is to reduce or eliminate the use of herbicides by supporting non-chemical control methods. As part of the program, physical, biological, and cultural control methods have been prioritized above the use of chemical controls. However, certain populations of weeds have boomed during the recent drought that non-chemical methods cannot feasibly address. Therefore, some SPMs begin with a combination of implementing soil health practices and the use of a chemical approach to managing these species and will transition towards a non-chemical approach over time. This is a necessary step given the extreme challenge of managing and eradicating some of these weed species.

The success of the program will be evaluated based on the number of local ranchers engaged within the program, the number of SPMs developed as well as the acreage managed. If successful, the program has the potential to be extended to all agricultural lands in the coming years.

Driving through the Chileno Valley today, it’s difficult to witness thousands of acres inundated with these invasive plants. Dense stands of weeds are beginning to change the soil chemistry such that other species can no longer grow and, unable to graze livestock, fuel loads continue to build amid the summer dry season. Huge swaths of this prime agricultural lands have been weakened to the point they struggle to capture and store planet-warming greenhouse gasses, improve ground water infiltration, and sustain the region’s wide range of biological diversity.

With impacts so far ranging, solving this crisis is only possible with a collective effort and a willingness to be as creative as the weeds themselves.


Stefan Parnay
Department of Agriculture, Weights and Measures

1682 Novato Blvd.
Suite 150-A
Novato, CA 94947
(415) 473-6700
Email: Stefan Parnay
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