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Other Invaders

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Curlyleaf Pondweed is moving in Curlyleaf Pondweed is moving in

Area waterways boast a plethora of invasive plant species

Though Eurasian Watermilfoil receives a lot of press these days, there are other nasty aquatic invasive species present in our region. Eurasian Watermilfoil (Myriophyllum spicatum) certainly leads the pack in largest acreage covered, but the threat of the other invaders looms high. Maybe not as sexy as Eurasian Watermilfoil, Flowering Rush (Butomus umbellatus), Curlyleaf Pondweed (Potamogeton crispus), Yellowflag Iris (Iris pseudacorus), and Purple Loosestrife (Lythrum salicaria) will require our undivided attention, too.

When aquatic invaders move into a new territory, they put the entire region at risk, most notably due to boat traffic and movement through the Pacific Northwest. Most of the aquatic invaders have been slowly marching from the East Coast across the nation to the West. It becomes imperative to educate natural resource managers, water users, and the general public on ways to prevent the spread of undesirable species that pose severe threats to the entire ecosystem.

Upstream of the Clark Fork River, Flathead Lake has a fairly serious infestation of Flowering Rush; this species has also been identified in Lake Pend Oreille. Flowering Rush is believed to have been introduced as a garden plant; though it can be an attractive plant, when released it can form dense stands that take over native plant habitat and impede recreational use of water bodies. Flowering Rush is easiest to identify when flowering; flowers grow in umbrella-shaped clusters and each individual flower has three, whitish-pink petals. An extensive root system provides the plant with new reproductive opportunities if disturbed, so control of this species is difficult. Flowering Rush in the region is noted to be about "head high." There are both emergent and submergent forms, with the latter producing vegetatively, and the former producing flowers; only one to five percent of the species present in the region is said to flower.

At Flathead Lake, Flowering Rush is documented as fairly dense, with an estimated 200 acres presently. Flowering Rush was first identified in Flathead Lake in 1964, and suspected to be an escapee from somebody’s water garden. Flowering Rush now colonizes the drawdown zone at Flathead Lake, which is the top ten feet of water. Due to the timing of lake level fluctuations, Confederated Salish Kootenai Tribes Wetlands Conservation Program Coordinator Sue Ball says there is nothing native to contend with Flowering Rush. "[Flowering Rush] is capable of out-competing all of our native plant communities," she says. "It is a northern tier problem, it appears," with Minnesota and Manitoba the leading regions with heavy infestations.

The CSKT, the tribal college, and the University of Montana are working together currently on a Flowering Rush study that will look at the biology of the plant as well as viable control measures. There will be an herbicide trial on the plant this spring, and also projects on the impacts of bottom barriers and hand-digging to the plant. Ball says that in certain places in Flathead, the Flowering Rush problem has been made worse by improper hand-digging attempts. If the stalks are pulled, the rhizome buds are released, which float off to create new infestations.

"You must control and contain all fragments or you make the problem worse," Ball says of Flowering Rush. "It doesn’t take much, like most other aquatic invasive species, to make a new plant."

They also have Yellowflag Iris, Purple Loosestrife, and Curlyleaf pondweed at Flathead Lake. Because they get a lot of inter-state boat traffic, Ball says that there is serious concern that Flathead will become infested with Eurasian Watermilfoil.

Yellowflag Iris is the only yellow iris found in the United States. The plant is four to six feet in height, and has a robust stalk and long, dark green, flattened, sword-like leaves. Yellowflag Iris experiences a long blooming season in the region. The plant is slowly spread and easily contained. It is spread by wind and water. The wind catches the seed and blows it into the water and the water carries it downstream to its new home.

Yellowflag Iris lives along stream beds, near ponds, and in marshes. It is popular with residential water gardens, and is regularly sold in nurseries, and from gardening websites. Until the sale of this invasive is curbed, it will continue to spread through the West; it is a fast growing plant.

In the Noxon Rapids and Cabinet Gorge Reservoirs on the Lower Clark Fork River in Montana, Eurasian Watermilfoil was identified last year, making Wyoming the only state in the U.S. without reported infestations. "We are aware of Eurasian Watermilfoil in the lower two-thirds of Noxon Reservoir," says Avista’s Recreation Specialist Brian Burky. "It is also found in Cabinet Gorge Reservoir intermittently in low numbers."

There is now a Sanders County Eurasian Watermilfoil Task Force, with nearly 20 individuals participating and representing a wide berth of organizations and interests. This summer, reports Burky, the Task Force has plans to begin scientifically mapping and quantifying the Eurasian Watermilfoil infestations. In addition to milfoil, Burky reports that there is Yellowflag Iris and Curlyleaf Pondweed in the reservoirs.

Avista holds license to two hydroelectric projects on the lower Clark Fork River at Noxon Rapids and Cabinet Gorge; the company manages most of the land adjacent to the reservoirs. Avista is intimately involved with the identification, management, and control of aquatic invasive species on project lands; they are also part of the task force.

"The task force has really come together," says Burky. "They are a good group of folks with lots of expertise at the table."

Further downstream, the Pend Oreille system has the largest infestation of Eurasian Watermilfoil in the region. Last year, during an extensive aquatic plant survey, Flowering Rush, Curlyleaf Pondweed, and Purple Loosestrife were also discovered.

"Curlyleaf Pondweed, for the most part, hasn’t caused a lot of problems in the West," says Aquatic Invasive Species Coordinator for Idaho Department of Agriculture Tom Woolf. "It likes turbid, high-nutrient waters, which we just don’t have a lot of yet."

Curlyleaf Pondweed is a submersed aquatic perennial with submerged leaves. This species has small "teeth" visible along edge of leaf; it begins growing in early spring before most other pondweeds, but dies back during midsummer. The flower stalks, when present, stick up above the water surface around August in the Pend Oreille system. Curlyleaf Pondweed appears reddish-brown in the water, but is actually green when pulled out of the water and examined closely. This plant is relatively easy to identify given the "crinkled" leaves; the mature leaves have a distinct lasagna noodle appearance.

Curlyleaf pondweed is a highly competitive plant, proficient at rapid growth and spread. Infestations may displace native species, reduce biodiversity, impede recreational activities, and reduce property values. As the dense mats of vegetation decay, available oxygen in the water may be depleted. The resulting anoxic (low oxygen) conditions may lead to fish kills and harm other aquatic organisms. Nutrients released from the decaying plant matter can also be a problem in water bodies with high nutrient levels. Curlyleaf Pondweed is found throughout the Pend Oreille system, most notably in the River, where it has adapted very well to river conditions and flow. It is the only non-native pondweed found in the United States.

"In the East, Curlyleaf Pondweed often turns lakes to nasty green pea soup pools," says Woolf. "It’s definitely a concern [here], but not to the same extent at time." This species is currently not included on the Idaho Noxious Weed List.

Flowering Rush was recently discovered in the Clark Fork Delta, right at the confluence of the Lower Clark Fork River and Lake Pend Oreille; the infestation is estimated to be about eight acres. There is some interest to pull together a volunteer effort to train folks how to dig the roots from the lake bottom; this project would have to take place in the fall following drawdown when the plants are more accessible.

Purple loosestrife is an erect perennial herb with a square, woody stem and opposite or whorled leaves. Leaves are lance-shaped, stalk-less, and heart-shaped or rounded at the base. Loosestrife plants grow from four to ten feet high, depending upon conditions, and produce a showy display of magenta-colored flower spikes throughout most of the summer. Flowers have five to seven petals. Purple loosestrife enjoys an extended flowering season, which allows it to produce vast quantities of seed. The flowers require pollination by insects, for which it supplies an abundant source of nectar. A mature plant may have as many as thirty flowering stems capable of producing an estimated two to three million seeds per year. 

Purple Loosestrife adapts readily to natural and disturbed wetlands. As it establishes and expands, it outcompetes and replaces native grasses, sedges, and other flowering plants that provide a higher quality source of nutrition for wildlife. The highly invasive nature of Purple Loosestrife allows it to form dense, uniform stands that limit native wetland plant species and reduce habitat for waterfowl. There is a beetle biocontrol agent that is said to be an excellent control mechanism.

Bonner County has a designated "Aquatic Invasive Species Task Force" that is comprised of 15 diverse stakeholders, representing various organizations, agencies, and individual interests. The role of the task force is to advise the county commissioners on the control, prevention, and spread of aquatic invasive species; the focus to date has been on Eurasian Watermilfoil. The task force is currently in the throes of writing a strategic plan for aquatic invasive species, so ideally this will help prevent the other invaders from spreading and new ones from entering the system.

Ultimately, if the spread of aquatic invasive species is to be curbed, the issue will need to be addressed on a regional level. Pathways of invasion need to be tracked to find out where boaters and other recreationalists come from, how often they use the water, and how much they know about aquatic invasive species transportation and impacts to native plants, fish and wildlife, and public enjoyment of the resource.

"Collaboration, education, and prevention are critical to the success of any project, especially when dealing with invasive species," says Woolf.

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Author info

Kate Wilson Kate Wilson was a Project Journalist for Avista's Clark Fork Project. She has been interested in environmental issues since she was a youngster.

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