Specialists from the Snohomish County Noxious Weed Board on Sept. 3 are scheduled to start the process of eradicating an infestation of common reed (Phragmites australis) at the Edmonds Marsh. Phragmites is a noxious weed requiring control in Snohomish County. The effort will be the first step in restoring native plant communities in areas degraded by the infestation, and will bring the City of Edmonds into full compliance with Snohomish County law.
Phragmites is a highly invasive grass that forms a dense monoculture in wetlands, altering the structure of local ecosystems, reducing biodiversity, and degrading habitat quality. Two Phragmites patches have been identified in the northern part of the marsh and will continue to spread through a dense underground network of rhizomes if left untreated.
According to a City of Edmonds announcement, initial treatment of Phragmites will consist of manual “spot” applications of Imazapyr, an herbicide categorized by the EPA as practically non-toxic (the lowest toxicity category) to fish, invertebrates, birds and mammals. Spot application means that the herbicide is applied only to the target plants, avoiding surrounding plants and soil. If strong wind occurs, application will stop to prevent the herbicide from drifting to unintended locations.
According to Snohomish County Noxious Weed Control Coordinator Geraldine Saw, “approximately 90% of the Phragmites is expected to decrease after treatment. After Phragmites has been reduced, nearby native marsh plants including Baltic rush (Juncus arcticus), Lyngbye’s sedge (Carex lyngbyei) and seashore saltgrass (Distichlis spicata) are expected to naturally re-colonize the treated areas.”
The county’s field team plans to conduct follow-up surveys and additional treatments when necessary. During their Sept. 3 visit, the team will also treat Japanese knotweed (Polygonum cuspidatum), another invasive plant that is challenging to eradicate manually.The eradication effort is consistent with the City of Edmonds Integrated Pest Management (IPM) approach to parks maintenance, which prioritizes the use of physical, mechanical, and biological control methods. Chemical treatments are used only when other control efforts would not be effective, as is the case with the current infestations of Phragmites and knotweed.
You can learn more about how the city manages plant and animal pests in parks by visiting Edmondswa.gov and searching for IPM.