Battle on invasive watermilfoil in Noxon shows success

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In 2012, the Sanders County Aquatic Invasive Plants Task Force waged the largest battle thus far in the war against two species of non-native weeds in the Noxon and Cabinet Gorge reservoirs -- Eurasian watermilfoil (EWM) and curlyleaf pondweed (CLP). Noxon Rapids Reservoir contains the uppermost known infestations of EWM on the Clark Fork River drainage.

EWM is an extremely aggressive non-native weed that poses threats to lakes and rivers. Once introduced into a water body, it quickly spreads and forms thick beds with dense canopies that crowd out native aquatic plants. Infestation threatens water quality, fisheries, drinking and irrigation water supplies, recreational uses and hydroelectric operations.

In the 2012 effort, just over 172 acres within Noxon Reservoir were treated with aquatic herbicides. Post-treatment surveys, both from the air and within the water, yielded good to excellent results, between 80 and 95 percent efficiency. Control was highest in large blocks and slightly less effective in narrow, shoreline plots.

Following their Integrated EWM Management Plan, the task force’s attack continued use of bottom barriers at targeted public boat dock and private facilities. Similar to garden “weed block,” the barriers prevent fragmentation of the plant by boat propellers, which is a primary method for spread.

Other measures continued in 2012 were boater education and outreach, including signage, promotional items and personal contacts; and outreach through use of boat cleaning and inspection stations.

Herbicide Treatments

John Halpop, task force chairman and Montana State University Extension Agent in Sanders County, is pleased. “Control results paralleled what we learned in the research phase of this project,” he said. “We learned a lot in the first couple of years.”

EWM was first discovered in the system in 2007. From 2008 through 2010, the task force formed and initiated measures to rein in the aquatic species.

In 2009 and 2010, with the help of invasive plant specialists Dr. Kurt Getsinger of the Army Corps of Engineers, and Dr. John Madsen of Mississippi State University, the group undertook dye and aquatic herbicide test plot studies. They learned how to predict the water flow characteristics using dye, then initiated herbicide treatments to determine the rate of herbicides and contact time necessary to control both EWM and CLP.

The herbicide application was guided by GPS to deliver the exact dosage needed at coordinates where infestations were located.

“Everything’s got to be just right,” said Forest Service botanist and weed manager Terry Hightower, vice chairman of the task force. Hightower and others learned the intricacies of tackling EWM and CLP in a moving, multi-dimensional water column.

In 2011, the task force was ready to transition from the research, to an operational phase, treating up to 200 acres on an annual basis, as significant funds awarded from a Department of Natural Resources and Conservation’s Reclamation and Development grant and the Montana Department of Agriculture’s Noxious Weed Trust Fund, would allow.

Due to species variation and growth patterns, it has been possible to target EWM, while allowing native species to repopulate the sites. Necessary environmental assessment and permitting was in place, but a late winter and high run-off didn’t present the proper conditions to conduct active treatment.

Then, in 2012:

Herbicides were applied by Clean Lakes, Inc., of Coeur d’Alene, Idaho, a firm that meets all required certifications and qualifications, and has state-of-the-art equipment and experience to undertake the work. Herbicides were applied in accordance with EPA and Montana Department of Environmental Quality requirements.

Clean Lakes, Inc. coordinated the treatment application with Avista and the task force. Treatment was done in early August with optimal weather, river flows and timing of weed growth. Work was done at night to minimize water movement; power generation at the Noxon Dam was shut down.

Prior to treatments, weed beds were monitored by Aquatechnex, of Bellingham, Wash., to determine the amounts and locations of native and non-native weeds. Information was used to finalize the plan for exact areas to be treated.

The plant community was assessed one month after treatment. Again, in summer 2013, one year after herbicide application, Aquatechnex will monitor the treated areas to determine effectiveness. The firm, with guidance of Dr. Getsinger, will survey and recommend areas to be treated in 2013.

“The 2012 treatments appear to be successful,” said Hightower.

“The Noxon and Cabinet Gorge reservoir system currently has less than three to four percent of Eurasian watermilfoil. EWM hasn’t gotten a big hold yet, so our goal is to continue to treat the larger stands,” said Halpop. “Eradication may not be realistic, but we want to reduce infestations of EWM to maintenance levels. The reservoirs are very important for ecological and environmental reasons, to a lot of people. Through the Environmental Assessment process, it was apparent that a ‘do nothing’ policy wasn’t an acceptable option for the future.”

Bottom Barriers

As a major partner since 2007, Avista placed approximately 25,000 square feet of bottom barriers at key locations along the Noxon and Cabinet Gorge reservoirs. Private individuals participated on a cost-share basis.

The barriers were provided with funding assistance by the Clark Fork Settlement Agreement and the Noxon-Cabinet Shoreline Coalition.

“The barriers are labor intensive to install, and especially to remove, when laden with mud and silt. They are also expensive, but worth it,” said Danny MacKay, Avista natural resources technician, who oversees the process.

It takes two divers and five other people, to do the twice-a-year job, carefully placing the 10’x10’ gas-permeable fabric, held rigid over EWM by sand-filled frames of PVC piping.

“The task force is making steady progress. Up and down the North Shore, it looked the best it has looked in many years,” said adjacent landowner Jim Marshall, who has been involved in the task force since its beginning.

Marshall has used bottom barriers since 2008, when Avista started the program. “They’ve made a big difference,” he said. “You’ve got to have both of them (barriers and herbicide treatments) to enjoy recreation at your dock.”

Boater education and outreach

Sanders County, with funding assistance from Avista and the Montana Noxious Weed Trust Fund, hired an education coordinator for the 2012 recreation season. Visitors were contacted at recreation areas and quizzed on their knowledge of EWM and its spread, receiving prizes for participation.

Of 244 questionnaires completed, 97 percent of those responding said that they clean, drain and dry their boats before moving them. An average of 32 percent said they could identify EWM, a figure which has risen 229 percent in the last five years. Ninety-six percent said they know that the weed spreads by fragments.

Contaminated water craft are the principal method of invasive aquatic spread.

Montana Department of Agriculture (MDA), with financial assistance from Avista, continued administering a program of inspection stations at key intersections where boaters enter or depart recreation sites in 2012. Montana Fish, Wildlife and Parks will administer and fund the stations in 2013.

Stations included those at the intersection of Hwy. 200 and Hwy. 28 at Plains; the junction of Highways 200 and 56 near Noxon; and at the intersection of Hwy. 56 and Hwy. 2 near Troy.

Last year, an increased number of boats passed through the check stations at Troy, Plains and Noxon, although it was found that less than 1 percent of checked boats were contaminated with EWM or other invasive species. MDA aquatic plant science specialist Craig McLane attributes the increase in contaminated species that were discovered, to be a combination of improved detection at stations, and increased movement of boats through areas where weeds were infested.

Boats are given visual inspection. If contamination is found, they are quarantined and thoroughly cleaned before they can be taken from the station.

“We want to check and make sure that plants (EWM and other invasive species) do not leave here and are not brought in with a contaminated boat or trailer,” said McLane. “The inspections take less than five minutes and the boaters can be on their way. It’s a small price to pay to help ensure Montana waters stay aquatic invasive species free.”

“Every single contaminated boat or trailer could’ve caused a new infestation in Montana, or in another state,” McLane added. “We hear more frequent support from boaters, who understand that the introduction of any of these aquatic invasive species may alter the way they are able to enjoy their favorite waters, which could even include lake closures.”

Boat Check Station Data, 2011:

-- Noxon: 1 (EWM) contaminated; 485 inspections.

-- Plains: 3 (1 EWM, 1 invasive flowering rush, 1 Zebra/Quagga mussel) contaminated; 954 inspections.

-- Troy: 5 (EWM) contaminated; 799 inspections.

Boat Check Station Data, 2012:

-- Noxon: 21 (10 EWM, 11 CLP); 2,081 inspections.

-- Plains: 9 (4 EWM, 4 curlyleaf pondweed (CLP), 1 invasive flowering rush); 3,504 inspections.

-- Troy: 4 (EWM) contaminated; 4,212 inspections.


Cost of the 2012 program totaled $389,197. In addition to major funding from a Montana Department of Natural Resources and Conservation Reclamation and Development grant and the Montana Department of Agriculture Noxious Weed Trust Fund, other partners were Avista, Montana Department of Agriculture, Montana State University Extension, Noxon-Cabinet Shoreline Coalition, Dr. Kurt Getsinger (U.S. Army Corps of Engineers), Sanders County, and Sanders County AIP Task Force.

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