Ludwigia Treatment Resumes September 13 in Slough


​Please use caution around the Willamette Slough at Minto Brown Island Park this coming week as spraying to control Ludwigia (Ludwigia hexapetala) resumes.

We're working with Willamette Riverkeeper to stop the spread of this aggressive, invasive water plant that has gained a stranglehold on the Willamette Slough, hurting recreation opportunities and wildlife alike. 

We ask park visitors to stay on the main trails and not try to access the slough during the period of active treatment.


This is a follow-up to treatments that occurred in late July, and will take about a week to complete. The contractor, IRM, will be spraying herbicide from canoes and the shore September 13-17. Treatment will start near the slough mouth and move south. We expect the majority of work to be complete Monday and Tuesday.

Willamette Riverkeeper will be providing more information at Riverfront Park on Monday, September 13.

The Willamette Queen will remain open during treatment.

Ludwigia, also called Uruguayan water primrose, forms dense mats in slow-moving backwater channels, oxbow lakes, and sloughs. While this yellow-flowered plant may appear quite pretty, it has the potential to choke entire waterways, severely restricting recreational access, degrading water quality, and creating an environment that is unfriendly to native fish and wildlife.

Up and down the Willamette River, groups are working to stop the spread of this highly invasive plant. The City of Salem and Willamette Riverkeeper have teamed up to do the same in the Willamette Slough. This three-year project aims to control Ludwigia in the slough through the careful use of an aquatic-approved herbicide sprayed on the plants by state-licensed applicators. 

The goal is to reduce the plant's population to such a degree that additional herbicide treatment will not be necessary once the project is complete. In the future, any new or remaining Ludwigia will be controlled by hand-pulling.  

This is the second of three years of treatment in the slough. The impact is already quite noticeable, with the extent of Ludwigia in the slough now substantially reduced from what it was  before the first treatment. The Willamette Slough will undergo its third and final year of treatment in the summer of 2022. 

Recreational users are advised to steer clear of the slough while treatment is in progress and for 24 hours after the last scheduled treatment day to limit potential exposure to the herbicides and to ensure maximum treatment effect. Treated plants will show signs of a blue-green dye, which is mixed with the herbicide so that applicators can see where it has been applied and reduce the amount of herbicide needed for control efforts.

Funding for this project was provided to Willamette Riverkeeper by Meyer Memorial Trust and Bonneville Power Administration. Learn more about Willamette River habitat restoration efforts and why projects like this matter with this storymap.   

Additional information about restoration efforts in the Minto Brown Island Park Conservation Area can be found on our website

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Clean StreamsNatural Resources Outreach Public Works Department
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