Launching the battle against fragrant water-lily

The word on the street in the Seeley-Swan is that the Missoula County Weed District may grab the bull by the horns and implement management tactics to control the prolific aquatic invader. Common sense generally persuades the wise to side-step such audacious gossip; however, the rumors are true and the process has already begun! Of course, in this case, the proverbial bull isn't necessarily a cantankerous 1,200-pound Spanish fighting bull, but rather the alluring perennial aquatic plant species commonly known as fragrant water-lily (Nymphaea odorata).

Gazing out from the shores of Seeley Lake, the seas of vibrant white fragrant water-lily (FWL) flowers perched delicately on the water's surface, near their impressive lily pads, may give off a regal, even tranquil, ambiance. However, this ambiance is simply a ploy which has allowed the introduced non-native FWL to establish and flourish within Missoula County's lakes and rivers since its introduction to Salmon Lake in 1937.

FWL is a perennial aquatic plant that can be easily identified by its heart-shaped leaves, fragrant flowers and at least 17 white-colored petals. Complications from this invader's presence include creating large dense monocultures that have the potential to choke-out and impede water flow in both lakes and slow-moving river systems, like the Clearwater. These large monocultures, which can reach several acres in size, are the culprits for two swim-related deaths within the state of Washington; additionally, the dense vegetation can foul the motors and hulls of boats.

To combat the presence of FWL, and its associated issues, Missoula County Weed District was recently petitioned by the Flathead National Forest to list FWL as a noxious weed species. In an effort to support the listing of FWL, Weed District staff has begun two large-scale projects with the intended goals of providing sound research and safe management practices for the general public.

The first project, which is currently ongoing, consists of four unique objectives to determine:

1. The full scope of the FWL population

2. The presence of other, native lily species within Missoula County

3. Best potential management options

4. Monitoring and water quality sampling of application sites

Objective one yielded rather interesting results with mapping efforts finding significant populations of FWL on eight of the 19 water bodies within the Clearwater and Swan drainages. Lakes with significant populations of FWL included Holland, Inez, Seeley, Placid, Salmon, Black, Elbow and Blanchard Lakes. Objective two determined that native lily species were present and subsequently mapped on almost all waterbodies within the region.

Objectives three and four are currently in progress and consist of small-scale herbicide applications to FWL within three lakes (Blanchard, Black, Salmon) as well as water quality sampling and monitoring. Herbicide applications (objective 3) took place this past August and comprised of three herbicides that are rated for safe aquatic use and are highly recommended by the Army Corps of Engineers.

As for objective 4, monitoring and sampling efforts are currently an ongoing process. Monitoring efforts evaluate the percent coverage of FWL after the herbicide has been applied to its respective subplot. Evaluation of the coverage will occur at three different timeframes; pre-treatment and two post-treatment observations. Pre-treatment observations indicate that current cover class is 100% for each plot. The post-treatment observations will take place exactly one month and one year after the initial application.

Water samples were also taken following the applications to determine the presence/absence of herbicides within the water column. These samples were acquired both above and below the thermocline (steep temperature gradient) of each lake, as well as in the central portions of the treatment plots. Two additional samples will be taken upstream of the three lakes to provide a basic foundation as to if herbicide is currently present within the aquatic systems. Additional quantitative data (temperature, pH, dissolved O2, etc.) will be measured and observed at a monthly interval.

The second large-scale project proposed by the Missoula County Weed District focuses more on ecological research rather than management recommendations. This ambitious project has three primary objectives:

1. Quantify the changes in native plant communities as a result of non-native FWL infringement

2. Assess and quantify the long-term impacts that FWL has on water quality (pH, dissolved oxygen, chlorophyll and temperature) in aquatic habits

3. Develop genetic lineage tracing to evaluate the history of biogeographic distribution and spread of FWL and its reproductive mode currently present within the Pacific Northwest.

Research sites for objectives 1 and 2 will take place on four lakes within and near Missoula County (Placid, Upsata, Seeley and Blanchard). Sampling locations for objective 3 will span five western states: Montana, Idaho, Washington, Oregon and California.

The pinnacle of all of the above research is to provide an accurate listing of fragrant water-lily as a noxious weed species within Missoula County, as well as providing sound management advice to applicators who may treat the species in the future. Scientific research may be an effective tool to fight the presence of FWL.

However, little can be achieved without the even greater tool that is public support and comments. We would love to hear from you in regards to this project so please feel free to reach out to me at the Missoula County Weed District office with any comments, or for information on the progress of the projects. Email me chris@missoulaeduplace.org for more information.