Boaters Beware

This is the first article in a two-part series on noxious weeds I wrote at the beginning of my tenure at the Leader.  Invasive weed species, if not managed, could have irreparable effects on this agriculture-based economy.

FLATHEAD LAKE — They come in small numbers and slowly take over everything in their path. As they ruin the lives of natives, they leave the landscape changed for the worse. It’s not a rebel army or a plague of locusts; it’s noxious weeds.

And they are waging their own biological war.

According to the Montana Weed Control Association, Montana currently has 32 state-listed noxious weeds in every county of the state. Western Montana has a much larger problem given population densities where weeds are primarily spread through travel vectors.

In Lake County, residents see the brunt of the problem.

“We’re pretty inundated with noxious weeds,” Tom Benson, director of Lake County Weed Control, said.

Benson said no single entity has the budget to deal with noxious weeds and that education is a key component in preventing the spread of weeds. What needs to happen is a bridging of the gap between education and weed control, he said.

Aquatic invasive species have taken the forefront of the noxious weed discussion. While many residents of Lake County are aware of the eminent threat of zebra mussels, two lesser-known menaces are plaguing Flathead Lake.

An early infestation of curlyleaf pondweed, classified as Potamogeton crispus, has been found in the north half and several pockets of Flathead Lake, said Flathead Basin AIS consultant Erik Hanson.

The weed has distinct, two- to three-inch, blue-green leaves that are wavy like lasagna noodles, Hanson said. Curlyleaf pondweed can grow in dense patches that displace native plants, which in turn displaces native animals and organisms dependent on those species.

“It’s like changing a meadow to a lawn,” Hanson said.

If a patch becomes too thick, fish can no longer move through it. If the weed keeps growing, Hanson said it might begin to interfere with recreation.

Management agencies are attempting to remove the weed using a minimally intrusive method called mechanical diver dredge, also known as suction harvesting. Hanson explained that a diver swims to the bottom of the lake and hand pulls the weed then feeds the weed through a suction tube back up to a boat.

There are six bays in Flathead Lake that show signs of curlyleaf pondweed, and Hanson said divers have yet to examine the lake to gauge the exact acreage the weed is affecting. Depending on thickness, it will cost $1,000 to $5,000 per acre to remove the species. Hanson estimated there are currently 10 acres of Flathead Lake infested with the weed.

Funding has been provided by several grants to pay for eradication of the aquatic invader. The Flathead Basin Commission, the Flathead Lakers, Lake County and the Lake County Conservation District collaborated to get rid of curlyleaf pondweed.

Boaters can help stop the spread of curlyleaf pondweed by pulling weeds off propellers when they have gone through a patch of the weed. If they do this before heading to a different bay, Hanson said the weed could be kept isolated.

The outlook for the next invader is much more grim.

Flowering rush, Butomus umbellatus, now occupies thousands of acres of Flathead Lake, Hanson said.

Its umbrella-shaped clusters and three whitish-pink petals with triangular stems make the plant identifiable. What makes flowering rush so dominant is the ease with which it spreads. Once disturbed the plants will rise to the surface of the water, then float to another section of the lake where they will spread seeds and take root.

Infestations are so significant and widespread that mechanical techniques would be too expensive. Additionally, there are no aquatic herbicides on the market that are effective against the weed. Since there is no successful management tool to stop flowering rush, the weed has made an impact on the entirety of the lake.

The weed increases sedimentation rates, which makes shallow waters even shallower. Though it grows thinner than curlyleaf pondweed, flowering rush is believed to boost the numbers of non-native fish species by providing them a habitat to thrive versus native species that are struggling to maintain a presence in the ecosystem.

The weed has been present in the lake since the first report in Peaceful Bay near Lakeside and in 1964. Experts believe it was brought in on equipment.

Researchers, including Virgil Dupuis of Salish Kootenai College, are studying treatment technologies to manage flowering rush. The latest research trials found one treatment that proved effective against the intruder, giving hope to those who deal with the devastation the weed is causing.

Hanson is optimistic that an effective aquatic herbicide could be produced within the next several years. He said it would take time and an integrated plan to take care of such a prolific infestation, but he anticipates a change in the battle against the marine trespasser.

Next week, the Leader will be looking at terrestrial invasive weeds threatening our area.