War of the Weeds



While the Missoula City Council orders yet another appeasing round of weed management test plots, acres of knapweed, leafy spurge and dalmatian toadflax flourish on Mt. Jumbo, irrigated by late spring rains.

Just across the Hell Gate, those same rains are making Marilyn Marler’s job a little easier. Marler is the University of Montana’s integrated pest management specialist with the Sisyphean task of ridding UM’s 480-acre half of Sentinel of noxious weeds. This Tuesday evening, she and five volunteers are out taking advantage of the rain-soaked soil to attack a two-acre patch of St. John’s wort above the M.

From town, the St. John’s wort is a deep brown stain; up close, hardly any other plants grow in the thickest spots. Armed with gloves and long weed diggers, the group advances in a methodical line, pulling the new growth with last year’s seed pods still attached.

“I’ve always said this is what we should do,” says retired high school math teacher Don Rider as he yanks another clump. By evening’s end, they’ve cleared a quarter-acre or so—the equivalent of a football field from the end zone to the 25-yard line. There’s little left in their wake besides churned dirt, so volunteer Glenda Hammond will sow the area with donated grass seed later in the summer.

Photo by Photo by Chad Harder
U of M pest management specialist Marilyn Marler digs St. John’s wort from the front side of Mount Sentinel with a half-dozen volunteers. “It would be great if someone could put [the St. John’s wort] to use,” said Marler. “It brings a pretty good price.”

When Since Marler was hired to take on Sentinel’s weeds last November, she’s been building community partnerships. Her M-trail “adopt-a-switchback” program is already showing results. She points to nearly knapweed-free zones of grass dotted by blue lupine and pale yellow death camas. They were cleared by a host of different school and community groups in April.

The thing about hand-pulling, Marler warns, is that it is a commitment. Knapweed seeds can stay in the ground for up to 10 years before sprouting. “You can’t just show up to one weed pull and expect it to be gone,” Marler says.

Hand-pulling leafy spurge doesn’t do any good, as its roots can go down 30 feet. But in just two days last week, 10 of Missoula rancher John Stahl’s sheep, chaperoned by Zach the guard llama, ate out a nasty patch of spurge near the M trailhead. A few balsamroot plants, a little grass, and the lingering smell of sheep are all that remain. “There’s lots of public interest in grazing,” Marler says. “But it’s so steep and there’s no good water source.”

Stahl envisions the day when as many as 1,100 head of sheep roam both Sentinel and Jumbo all summer long. One or two sheep per acre would make sure they didn’t damage the soil or eat the natives. Although sheep are opportunistic grazers, they do prefer knapweed and will also seek out spurge once they get a taste for it, Stahl says. A major challenge for long-term grazing will be dog control. “If a dog gets into my herd, it stops being a pet and becomes a predator,” Stahl says, and the law would allow him to shoot the offender. Owners of two off-leash dogs that jumped into the sheep pen last week were fined.

Marler will attack still other patches of spurge with a weed-whacker. The idea behind both methods, Marler says, is to keep the plants from going to seed, and eventually exhaust their root reserves. This can take years.

Small but hungry flea beetles will be turned loose on the spurge in July when the adults emerge and can be collected. The larvae they spawn will bore into the plant’s roots and commence to eat.

And yes kids, there will be spraying on Mt. Sentinel. In the next two weeks, Tordon will be sprayed on isolated patches of spurge to keep the yellow-green, alien-looking flower from spreading into less-heavily infested areas.

“You have to focus on the places that are the least damaged first,” Marler explains. As for the use of herbicides, she says, “Mt. Sentinel is in such bad shape, I can’t see any way to avoid chemicals. I’m a botanist and I’m concerned about plant diversity. The herbicide issue is frustrating because people just reject it.”

Moreover, the University is under orders from the Missoula County Weed Board to review the 10-acre-per-year cap on spraying set down by a campus committee. The County says the limit may prevent adequate control efforts as required by state law. Marler agrees that the 10-acre rule is somewhat “arbitrary,” but hastens to add that there are no plans for aerial spraying.

Given that Marler is faced with nibbling away at 480 acres of weeds a quarter-acre at a time, it’s no surprise that she sums up her eclectic methodology thusly: “I’m open to all things. It would just be nice to get people involved in restoration.”

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