Control where it goes

Well, short of doing comprehensive scrubs of passing ducks and geese, the only way to minimize spread is to screen overflow pipes. That, and to quickly control it wherever you find it.

Control where it grows

• Dig: digging up water primrose is a lot of work. Plus, dug-up plants should dry out before being moved to prevent further spread. Alternately, plants can be composted on-site, if space allows. Specialized tools, such as the Lake Rake™, can be used to mechanically remove this and other aquatic plant species from the water surface.  Care should be taken, though, because each piece of stem can potentially create a new plant. 
• Treat: trials are currently being conducted in Portland and the Eugene area to find the most effective herbicide, rate, and timing. Aquatic treatment of herbicide must only be done by licensed applicators. Do not attempt this method on your own.
• Check: monitor the site at least annually, and especially years two and three after treatment, as any surviving seed takes its big opportunity to sprout!

Last Words

If you think you’ve found invasive water primrose, please contact Mitch Bixby with the Environmental Services' Early Detection/Rapid Response Program at 503-823-2989 or mitch.bixby@portlandoregon.gov.  Water primrose should be positively identified before management begins to prevent unintended damage to related native species. In any event, knowing about all patches helps area land managers plan and run their programs.  Assistance from the city may also be available.