Yellowflag Iris and Purple Loosestrife on the Clearwater River

In 2004 when the Missoula County Weed District initially mapped the infestation of yellowflag iris that had recently been reported to us on the Clearwater River between Salmon Lake and the Blackfoot River, we faced a daunting challenge: 10 miles of river, both banks heavily infested and nearly 83 acres of dense thickets peppered with yellowflag iris. The yellowflag iris was already beginning to fill-in shallow bays on Elbow Lake, degrade wetlands and river bank habitat on the Clearwater River and was threatening to spread onto the Blackfoot River. A partnership was formed with the Montana Department of Natural Resources and Conservation, Fish, Wildlife & Parks, the Missoula County Weed District and multiple private landowners along the infested stretch of river and we began a long-term effort to eradicate yellowflag iris from the Clearwater. As we enter our fifteenth season of mapping and spraying yellowflag iris on the Clearwater River that elusive goal of eradication finally seems achievable.

Yellowflag iris, a native of North Africa and Mediterranean Europe, was a popular ornamental flower before it escaped and began aggressively invading waterways and wetlands throughout North America, Europe and the British Isles. Spread by seeds or broken root fragments that float downstream, yellowflag iris poses a serious threat to the health of Montana's riparian and wetland habitats.

Yellowflag iris infestations form thick root-balls and dense vegetation that chokes out native plants. When native vegetation is removed, the once healthy wetland becomes uninhabitable for any other species besides yellowflag iris and its habitat value plummets.

The Missoula County Weed District began treating the Clearwater River yellowflag iris infestation in 2006 with the aquatically labeled herbicide Aquaneat®. The project has been funded through the Montana Noxious Weed Trust Fund grants program with significant matching funds from the Missoula County Weed District, DNRC and FWP. With a goal of eradication, we have had to develop innovative mapping techniques that combine intensive mapping with highly detailed field maps and modern GPS equipment that allow the herbicide applicators to locate and treat every known plant.

Much blood, sweat and yes, sometimes tears have been expended while crawling through the thickets of the Clearwater hunting for iris. Our success can be seen in the photos (above) taken since the beginning of the project and by the tremendous reduction in the amount of herbicide used each year: 10.12 acres were sprayed in the first year of treatment, which only treated the upper seven miles of the project compared to .08 acres treated in 2017 along the entire 10 miles of the project area.

In 2009 a new challenge emerged on the Clearwater River when purple loosestrife was first discovered. Like yellowflag iris, purple loosestrife is native to Europe and Asia and has made its way into the west as an intentionally planted decorative ornamental plant. A wetland plant, purple loosestrife spreads primarily by seed. Each plant can produce up to 2.7 million seeds annually.

As tiny as grains of sand, purple loosestrife seeds are easily spread by water, wind, wildlife and humans. We have had good success in killing purple loosestrife but every year we find new plants growing nearby the sites where we killed purple loosestrife the season before. We feel like we are holding the line on purple loosestrife and hope our continued efforts will start to reduce the number of plants we find.

We will be on the Clearwater River in the beginning of August hunting for the last surviving yellowflag iris plants and the scattered patches of purple loosestrife. If any of you see any yellowflag iris elsewhere in the Seeley/Swan, please let us know. Past reports of small iris infestations at the outlet of Seeley Lake have helped us keep the Clearwater River between Seeley and Salmon Lakes iris free. Contact Jed Little, 406-258-4220 or mapping@missoulaeduplace.org, to report any yellowflag iris or purple loosestrife you may stumble upon or if you have any questions about the project.