Starting Sept. 3, Snohomish County to treat invasive plants in the Edmonds Marsh

During a recent visit to the Edmonds Marsh, Geraldine Saw demonstrates the tough, fibrous stems and leaves of Phragmites that make it unsuitable for wildlife forage. (File photo by Larry Vogel)

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.

(Learn more in our earlier story here.)

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 and searching for IPM.


  1. I hope this careful herbicide helps.
    It’s unfortunate that Nightshade is not also classified as a noxious weed. Nightshade has badly reduced the flow of water under Hwy 104 from East into the West side of the marsh. This has blocked fish runs, allowed non-native species to flourish, and increased flooding on Dayton Street near the waste treatment plant.
    Joe Scordino has been organizing volunteer work parties to manually clear out Nightshade in an attempt to restore water flow. I’ve only been able to volunteer twice this season, but it was very personally rewarding work. Saturday will be the last volunteer party this Saturday until next year.
    Restoration of the Edmonds marsh is critically important for reasons too numerous to mention here.

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