2022 MKAT Update
Significant gains were made during 2022 to manage invasive Japanese knotweed in San Geronimo Valley. Of the 92 sites surveyed in 2022, 43 had no visible above ground stems. Of the 49 sites that did, 43 had fewer stems than in 2021. That is an improvement from only 30 sites that had a diminished stem count the prior year. As stem counts go down in number, the amount of time, money, and herbicides required are reduced.
Four new sites were detected, each with a stem count of less than 10. These sites were treated for the first time in 2022 and will be monitored in the future. When patches are treated the rhizome is weakened. Later, tall stems often regrow with multiple short or deformed stems which can result in stems counts that create the appearance of an increase, while actual biomass above ground is lower than the year before.
The drought conditions led to an advance in treatment dates from late August to early August. This adaptation is assured to catch the plant after flowering but before senescence when the plant goes dormant for the winter. This treatment draws the systemic herbicides into the rhizome underground, reducing or preventing further above ground growth and weakening the plant.
MKAT continues to educate and communicate with property owners to manage invasive Japanese knotweed. Monitoring and treatment of sites will continue in 2023. Continued community support of our efforts is key to success and the protection of native plants and fish. By working together in a coordinated manner across the watershed, we can secure the accomplishments being made in eradicating and managing knotweed on both private and public lands.
A symposium is planned for March 1st, 2023 to share our collaborative process, techniques, adaptations, lessons, and successes. Several management approaches will be discussed as well as larger questions about this invasive weed in differing climatic regions.
Together we learn and grow through collaboration and move closer to our goal of knowing where the knotweed is and working to limit its spread and eliminate it where possible.