Invasive Species Resources

Weed Treatment Calendar

One goal of Cooperative Weed Management Areas (CWMAs) is to create a space for organizations and agencies to partner together. The Weed Maintenance Calendar is one product of collaboration within the Clackamas, Clark, Multnomah, Washington (4-County) CWMA, supporting the Portland metro area.

Download it here: 2020 Integrated Weed Maintenance Calendar

Following a bond measure in 2013, Metro, Portland’s regional government and longstanding 4-County CWMA member, contracted with the City of Portland’s Bureau of Environmental Services (BES), also a 4-County member, to assemble a management calendar. The calendar would describe the current consensus about managing the weed species Metro staff expected to work on. Starting with King County’s weed management calendar, BES made adjustments based on interviews with local partners, and added some new summaries of the calendar. In 2014, the Weed Maintenance Calendar arrived. The tool was, and still is, intended to reflect the prevailing opinion for managing the most common situations. Each land manager still needed to make case-by-case management decisions, which might very well diverge from the calendar. That is how it should be. We intended the Calendar to be a starting point.

In 2019, the 4-County CWMA asked Metro to allow revisions for distribution to other land managers; Metro agreed. After a period of discussion (and also of pandemic), the Weed Maintenance Calendar has re-emerged. The revisions aren’t done, and won’t ever be. Consensus shifts. We see this as a living document, with the capacity to adjust. As noted above, we fully expect local conditions to require ‘a little more of this’ and ‘a little less of that;’ land managers interpret these conditions. But we hope this is a helpful resource, and a place where the discussion can continue.

While the Calendar might be useful to the general public, we note that professional land managers have a range of opinions about many of these topics. Given the range of organizational priorities, goals, and missions, that is to be expected. We urge folks who use this calendar to be aware of that range, and to build working relationships with local land managers: they are better able to advise you in your particular circumstances.

Looking ahead, we will ask the 4-County Technical & Scientific Review Committee to review this document each winter, and make changes as necessary. Please feel free to join the conversation, and watch for future updates.

If you have any suggestions for the calendar, please contact our Technical & Scientific Review Committee Vice-Chair, Justin Cooley (