A major issue facing the Edmonds marsh and its surrounding watershed is the presence of invasive species. There have been ongoing efforts to rid the area of these invasive plants, but problems still persist. An overview of 5 major offenders is below.
1. Common Reed, Phragmites australis
Common Reed is a Class B noxious weed in Snohomish County, where the Edmonds Marsh Watershed is wholly located, requiring control of the species. It is a highly invasive plant that forms dense monocultures in wetlands, posing a particular problem for the Edmonds Marsh. Its presence limits biodiversity and degrades habitat by limiting the growth of native grasses and cattails.
Common Reed has native forms in the US, but it also has an invasive form, which does not yet have an official taxonomic name because its relationship to other species has not been established. It can grow up to 13 ft tall and grows in dense mats of rhizomes, making removal a challenge. The invasive type forms denser mats than native forms.
In September of 2023, the Edmonds Marsh underwent treatment for two patches of Common Reed that had become established. Because of how the plant grows, herbicides are required to control growth. The team used an herbicide categorized as safe for fish and other animal species by the Environmental Protection Agency to limit harm to the ecosystem around the marsh.
2. Bittersweet Nightshade, Solanum dulcamara
Bittersweet Nightshade is another invasive plant affecting marsh health. It has overgrown paths, blocked water flow, and killed trees. It has also been impacting the creek runs that feed into the marsh by limiting water flow. Bittersweet Nightshade grows as a vine and is likely native to the UK and northern Europe. It is widespread across the northern US, and in the Pacific Northwest is found more in marshy areas near Common Reed.
Invasive Bittersweet Nightshade overgrowing and backing up Shelleberger Creek, which feeds into the marsh (left, source) and Bittersweet Nightshade overgrowing an access path at the marsh (right, source).
There were major efforts in 2021 and 2022 to remove nightshade from the marsh and creek runs flowing into the marsh. However, seeds are spread via birds that ingest the plant's berries. With the marsh being a major bird habitat, any Bittersweet Nightshade in the area risks new starts from seed in the marsh. The plant in North America is mostly found on disturbed sites, so as more work is done to restore the marsh to a natural state, the less likely recurrence will be.
3. Himalayan Blackberry, Rubus armeniacus
Himalayan Blackberry is widely distributed in Washington and is classified as a Class C Noxious weed, which allows county noxious weed boards to select species to control. Because Himalayan Blackberry is so widespread in Snohomish County, it has not been selected for control since the control required of selected species would be too high. With its thick thorns and complex root systems, Himalayan Blackberry can pose a real challenge to remove. This plant has been found in the marsh and along the creeks that run into the marsh. It often out-competes native plants and poses threats to wildlife.
Himalayan Blackberry is native to Armenia (not the Himalayas) and is widespread across the western US and Hawaii. It requires to or more years of persistent removal to achieve eradication in an area.
Work parties have made efforts to remove Himalayan Blackberry, but because it is not classified in Snohomish County there are fewer resources available for its control. Similarly to Bittersweet Nightshade, Himalayan Blackberry also spreads by seed from its berries, so reseeding is likely in the marsh.
4. Purple Loosestrife, Lythrum salicaria
Purple Loosestrife is a common invasive weed in wetlands and affects the Edmonds Marsh. It is a Class B noxious weed designated by the county and is quarantined in the state, meaning it cannot be sold or traded. It competes with native vegetation and has a persistent tap root. It provides poor coverage for waterfowl, making it a problem for the Edmonds Marsh.
Purple Loosestrife is native to Eurasia and was introduced in the US by settlers. It can regrow from root stock that is left in the ground, as well as spreading prolifically by seed. Digging up plants by the root can be effective, and there are herbicides available that are effective on Purple Loosestrife as well. Additionally, there are a number of insect species that target Purple Loosestrife that can be used as control agents. In the Edmonds Marsh watershed area, there were no recorded removal projects, but likely many previously-mentioned work parties have targeted this problematic species as well.
5. Japanese Knotweed, Fallopia japonica
Finally, Japanese Knotweed presents challenges across Snohomish County and Washington, as well as in the Edmonds Marsh. It is designated as a Class B noxious weed in Snohomish County and is a quarantined species. It can form dense stands, crowding out other vegetation and providing poor wildlife habitat. Once established, it is difficult to control since even very small fragments of the plant can root and grow. It is primarily established by spreading rhizomes, but can also spread by seed.
Japanese Knotweed is native to Asia and was brought to North America as an ornamental. It is established in the Edmonds Marsh, making removal a necessity before it spreads further. There was a work party in 2016 dedicated to removing Japanese Knotweed and there have been numerous community weeding events since which target these common invasive plants in the marsh.
References
General
Class B Weeds. (n.d.). Snohomish County. Retrieved October 30, 2023, from https://www.snohomishcountywa.gov/1750/Class-B-Weeds
Class B Weeds Designated. (n.d.). Snohomish County. Retrieved October 30, 2023, from https://www.snohomishcountywa.gov/1751/Class-B-Weeds-Designated
Facts and Features. (n.d.). Edmonds Marsh Estuary Advocates. Retrieved October 30, 2023, from https://www.edmondsmarshestuary.org/basic-facts-and-features
Common Reed
Snohomish County to treat invasive plants in Edmonds Marsh Oct. 2. (2023, September 26). My Edmonds News. https://myedmondsnews.com/2023/09/snohomish-county-to-treat-invasive-plants-in-edmonds-marsh-oct-2/
Tilley, D.J., and L. St. John. 2012. Plant Guide for common reed (Phragmites australis). USDA-Natural Resources Conservation Service, Aberdeen, ID Plant Materials Center. https://plants.usda.gov/DocumentLibrary/plantguide/pdf/pg_phau7.pdf
Bittersweet Nightshade
MyEdmondsNews. (2021, September 14). Community volunteers complete Edmonds Marsh restoration project. My Edmonds News. https://myedmondsnews.com/2021/09/community-volunteers-complete-edmonds-marsh-restoration-project/
Scordino, J. (2022, July 28). Edmonds Marsh restoration: Battle with invasive nightshade continues. My Edmonds News. https://myedmondsnews.com/2022/07/edmonds-marsh-restoration-battle-with-invasive-nightshade-continues/
Waggy, Melissa A. 2009. Solanum dulcamara. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: https://www.fs.usda.gov/database/feis/plants/shrub/soldul/all.html [2023, October 30].
Himalayan Blackberry
Himalayan Blackberry. (n.d.). Washington State Noxious Weed Control Board. https://www.nwcb.wa.gov/weeds/himalayan-blackberry
Stannard, M.E. 2014. Plant guide for Himalayan Blackberry (Rubus armeniacus). USDA-Natural Resources Conservation Service, Plant Materials Center, Pullman, Washington 99164-6211.
Purple Loosestrife
Purple Loosestrife. (n.d.). Washington State Noxious Weed Control Board. Retrieved October 30, 2023, from https://www.nwcb.wa.gov/weeds/purple-loosestrife
Urbatsch, L. (2019). Purple Loosestrife. USDA NRCS National Plant Data Center.
Japanese Knotweed
Heutte, T., Shephard, M., & Snder, C. (2007, August). Japanese Knotweed. US Forest Service. https://www.fs.usda.gov/Internet/FSE_DOCUMENTS/fseprd679422.pdf
Japanese Knotweed. (n.d.). Washington State Noxious Weed Control Board. https://www.nwcb.wa.gov/weeds/japanese-knotweed
MyEdmondsNews. (2016, June 3). Windermere agents tackle “knotty” problem at Edmonds Marsh. My Edmonds News. https://myedmondsnews.com/2016/06/windermere-agents-tackle-knotty-problem-at-edmonds-marsh/