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MILE 135, DALTON HIGHWAY — An occasional tractor-trailer rumbled by at 60 mph as Tom Balland, wearing a bright orange reflective vest, crawled around on the shoulder of the Dalton Highway near Prospect Creek pulling weeds.

The trucks, hauling equipment and supplies to the North Slope oil fields, are a common sight on the Haul Road, as the Dalton Highway is affectionately called by Alaskans.

So, too, is the weed that Balland was pulling.

It’s called white sweet clover, and it is one of 65 plants that has been identified as a non-native invasive species in Alaska.

“We missed one here,” Balland said, proudly displaying the small, green-leafed plant between his thumb and forefinger. “You can go through here 50 times and you’re still going to miss some.”

Dropping the plant, Balland resumed his search, combing the gravel as if he were looking for a contact lens.

“Here’s another one,” he said, triumphantly pulling up another of the tiny weeds. “And another one. And another one.”

For the last three years, volunteers like Balland, who works with a group called Friends of Alaska National Wildlife Refuges, have been pulling white sweet clover plants up along the Dalton Highway as part of a grass-roots effort to keep the weed from spreading into the Kanuti National Wildlife Refuge.

“What we want to do is keep it from getting into rivers and spreading west into the wilderness,” Kanuti refuge manager Mike Spindler said, as he helped Balland and three other volunteers yank up weeds during a visit on Tuesday. “Once the seed source gets in the river, the flood waters will spread it everywhere.”

There are six rivers that cross the Dalton Highway and flow into the 1.6-million-acre refuge north of Fairbanks — the Kanuti River, Fish Creek, Bonanza Creek, Prospect Creek, the Jim River, the South Fork of Koyukuk and the Middle Fork of Koyukuk.

Refuge officials are worried that white sweet clover will find its way into the refuge and take over gravel bars in the Koyukuk River drainage, Spindler said. It could out-compete willows, which are a valuable food source for moose, he said. Infestations of the weed have already been found on gravel bars on rivers in Southeast, Southcentral and Interior Alaska.

The U.S. Fish and Wildlife Service has been providing funding to the Bureau of Land Management for the past three years to pay for the weed-pulling effort. The BLM manages the land along both sides of the Dalton Highway north of the Yukon River.

“We’re spending $20,000 a year,” Spindler said. “That’s a pretty small investment, and it’s probably worth it until we do more research to figure out what we’re going to do if it hits gravel bars.”

Growing problem

On an “invasiveness scale” of 0 to 100 with 100 being the worst, white sweet clover scores “in the 80s,” according to BLM wildlife biologist Ruth Gronquist, who is leading that agency’s effort to control the spread of the weed.

The plant, along with its close cousin yellow sweet clover, was introduced to Alaska in 1913 as a potential forage crop, according to Jeff Conn, a research agronomist and weed scientist for the USDA.

Today, white sweet clover can be found along most of the road systems in Alaska from the Kenai Peninsula to the Brooks Range. It is common along the Parks, Richardson and Dalton highways and in most communities along the road system, including Fairbanks.

“You look around (Fairbanks) and you see it all over the place,” Spindler said.

White sweet clover jumped the Yukon River seven years ago and has been found as far north as Coldfoot, a Haul Road truck stop about 250 miles north of Fairbanks. Like most invasive plants, white sweet clover is “very opportunistic,” Gronquist said.

“I’ve only been looking at it on the Dalton Highway since 2004 but I can tell you it’s been an exponential spread,” she said. “Roads are perfect vectors for the spread of invasive plants.”

Dubbed “the pest with the pretty name,” white sweet clover has a two-year life cycle. The first year it develops a deep tap root and the second year it flowers and produces seeds. Each plant has the ability to produce as many as 350,000 seeds, making it extremely prolific. Roots of mature plants can be more than a foot long and resemble a full-size parsnip.

Invasive plants like white sweet clover are a growing problem in Alaska, where researchers are just beginning to catalog and study them. Invasive plants can shade out and replace native plants, changing entire ecosystems. White sweet clover, for example, adds nitrogen to the soil, which changes soil and plant chemistry.

So far, 65 plants have been identified as non-native invasive species in Alaska, including commonly found plants like dandelions, bird vetch, oxeye daisy, pineapple weed and foxtail barley.

“We’re finding more every year,” Gronquist said.

She leaned over and pulled up a yellow-flowering plant called narrowleaf hawksbeard that is becoming more common in Alaska.

“We call this the next dandelion,” she said.

Planting the seed

Rivers aren’t the only way white sweet clover could infiltrate the refuge, Spindler said. Airplanes and boats could also transport seeds into the refuge.

Last year, Spindler and a crew floated down the Kanuti River looking for white sweet clover on gravel bars and didn’t find any.

“This year we’re going to float the Jim River and the South Fork of the Koyukuk to look for it,” he said.

So far, the spread of white sweet clover has been limited mostly to roadsides and disturbed areas, such as construction sites. The weed flourishes in gravel, or what agronomist researcher Steve Seefeldt with the U.S. Department of Agriculture in Fairbanks called “basic soil.”

“Once it gets off the road bed it’s dealing with more of an acid soil,” he said. “Once it gets to acid soil and can’t make its own nitrogens, it sort of loses its advantages.”

While white sweet clover extends for more than 150 miles on the Haul Road, the weed-pulling effort has been concentrated at river crossings

In addition to pulling weeds, this year workers experimented by using weed whackers to remove and inhibit first-year growth. Another option that has yet to be tried is re-seeding areas with more aggressive native grasses to out-compete the weeds.

A two-week, weed-pulling campaign each year, though, isn’t going to be enough to prevent the spread of white sweet clover, Gronquist acknowledged. As she drove along the highway on Tuesday, Gronquist pointed out mature plant after mature plant.

“There’s a second-year plant,” she said, passing a four-foot-high flowering plant. “If we don’t pull that one, then next year there will be a one meter by one meter mat of seedlings under it.”

Making a difference

This is the fourth trip that Betty Siegel has made to the Brooks Range to pull white sweet clover along the Dalton Highway. Siegel is the volunteer coordinator for the Homer-based Friends of Alaska National Wildlife Refuges.

“It’s become a mission for me now,” Siegel said, crawling around near Prospect Creek searching for young plants on a cold, soggy day in the Brooks Range.

Siegel, a 68-year-old retired social worker who moved to Homer from San Diego three years ago, said programs like the weed-pulling effort allow volunteers to see different parts of the state while contributing to a good environmental cause. The BLM pays for volunteers’ travel, food and lodging expenses.

“I really do care so much about the refuges,” she said.

This is the first time Balland, a retired state sport fish biologist from Homer, joined the weed-pulling crew on the Dalton Highway. Balland, 56, is hopeful he and the others can make a difference.

“It’s something to be very concerned about,” he said. “Any of these invasive plants have the potential of totally changing the landscape as we know it, both flora and fauna.”

Last year, a team of about a dozen volunteers filled plastic garbage bags with 3 1/2 tons of white sweet clover, which was then burned.

After three years of weed pulling, Siegel is optimistic that volunteers are having an impact.

“I was down on my hands and knees redoing an area that I did a month ago and there were so many fewer plants and they’re pretty small,” she said.

Gronquist, too, thinks the weed pulling has made a difference, at least in the areas around the river crossings.

“We can’t eradicate it but we can contain it and almost eradicate it at river crossings,” she said. “We’ve been able to inhibit new growth.”

Seeking a solution

Even with all the volunteers in the world pulling up white sweet clover plants along the Dalton Highway, it would be practically impossible to stop the spread of the invasive weed, said Seefeldt, the researcher from the USDA.

“Eradication is a pipe dream” without using herbicides, Seefeldt said.

Part of the problem with pulling mature plants is that it disturbs the ground and distributes more seeds to grow. Seeds can live for up to 80 years in the ground before sprouting.

“Making sure there isn’t mature seed on the plant is critical,” said Seefeldt. “If you pull up one plant and 50 seeds sprinkle out, are you winning that battle?”

Researchers at the USDA have been experimenting with herbicides to see what works against white sweet clover and what impacts it might have on other plants and animals.

“There are some herbicides that we found that provide excellent control at very low rates,” Seefeldt said.

One of them is chlorsulfuron, which is commonly called telar.

“It doesn’t move much in the soil,” he said. “It stays where you spray it and it stays active for a long time, so any new seedlings germinating are killed.”

However, it will kill some native plants, Seefeldt acknowledged.

Scientists are hoping to see if moose will eat white sweet clover this fall at the Kenai Moose Research Center and determine whether or not moose pass the seeds through their digestive systems, Seefeldt said.

Scientists also are studying whether white sweet clover will colonize burn areas, of which there are several along the Dalton Highway and in the Kanuti refuge. So far, there has been no evidence the weed is sprouting up in burned areas.

The BLM is in the process of conducting an environmental assessment of the impact white sweet clover is having and composing a management plan to deal with it and other invasive species.

“We don’t know enough yet to know exactly what we’re going to do,” said Gronquist, who is on the Alaska Committee for Noxious and Invasive Plants Management.

But both Spindler and Gronquist said something will eventually have to be done to stop the spread of white sweet clover and other invasive species.

“I think eventually the public will understand we have to use herbicides,” Spindler said. “The question I have is how can we use them safely near water?

“If we can hold them at bay until we get the necessary research done, maybe we have a chance,” he said.