Battle is on with invasive white sweet clover

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MILE 135, DALTON HIGHWAY, Alaska An occasional tractor-trailer rumbled by at 60 mph as Tom Balland,wearing a bright orange reflective vest, crawled around on theshoulder of the Dalton Highway near Prospect Creek pulling weeds.
The trucks, hauling equipment and supplies to the North Slope oilfields, are a common sight on the Haul Road, as the Dalton Highwayis 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 hasbeen 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 gothrough here 50 times and you're still going to miss some."
Dropping the plant, Balland resumed his search, combing the gravelas if he were looking for a contact lens.
"Here's another one," he said, triumphantly pulling up another ofthe tiny weeds. "And another one. And another one."
For the last three years, volunteers like Balland, who works with agroup called Friends of Alaska National Wildlife Refuges, have beenpulling white sweet clover plants up along the Dalton Highway aspart of a grass-roots effort to keep the weed from spreading intothe Kanuti National Wildlife Refuge.
"What we want to do is keep it from getting into rivers andspreading west into the wilderness," Kanuti refuge manager MikeSpindler said, as he helped Balland and three other volunteers yankup weeds during a visit on Tuesday. "Once the seed source gets inthe river, the flood waters will spread it everywhere."
There are six rivers that cross the Dalton Highway and flow intothe 1.6-million-acre refuge north of Fairbanks - the Kanuti River,Fish Creek, Bonanza Creek, Prospect Creek, the Jim River, the SouthFork of Koyukuk and the Middle Fork of Koyukuk.
Refuge officials are worried that white sweet clover will find itsway into the refuge and take over gravel bars in the Koyukuk Riverdrainage, Spindler said. It could out-compete willows, which are avaluable food source for moose, he said. Infestations of the weedhave 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 tothe Bureau of Land Management for the past three years to pay forthe weed-pulling effort. The BLM manages the land along both sidesof the Dalton Highway north of the Yukon River.
"We're spending $20,000 a year," Spindler said. "That's a prettysmall investment, and it's probably worth it until we do moreresearch to figure out what we're going to do if it hits gravelbars."
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 wildlifebiologist Ruth Gronquist, who is leading that agency's effort tocontrol the spread of the weed.
The plant, along with its close cousin yellow sweet clover, wasintroduced to Alaska in 1913 as a potential forage crop, accordingto Jeff Conn, a research agronomist and weed scientist for theUSDA.
Today, white sweet clover can be found along most of the roadsystems in Alaska from the Kenai Peninsula to the Brooks Range. Itis common along the Parks, Richardson and Dalton highways and inmost 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 hasbeen found as far north as Coldfoot, a Haul Road truck stop about250 miles north of Fairbanks. Like most invasive plants, whitesweet clover is "very opportunistic," Gronquist said.
"I've only been looking at it on the Dalton Highway since 2004 butI can tell you it's been an exponential spread," she said. "Roadsare perfect vectors for the spread of invasive plants."
Dubbed "the pest with the pretty name," white sweet clover has atwo-year life cycle. The first year it develops a deep tap root andthe second year it flowers and produces seeds. Each plant has theability to produce as many as 350,000 seeds, making it extremelyprolific. Roots of mature plants can be more than a foot long andresemble a full-size parsnip.
Invasive plants like white sweet clover are a growing problem inAlaska, where researchers are just beginning to catalog and studythem. Invasive plants can shade out and replace native plants,changing entire ecosystems. White sweet clover, for example, addsnitrogen to the soil, which changes soil and plant chemistry.
So far, 65 plants have been identified as non-native invasivespecies 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 callednarrowleaf 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 therefuge, Spindler said. Airplanes and boats could also transportseeds into the refuge.
Last year, Spindler and a crew floated down the Kanuti Riverlooking 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 ofthe Koyukuk to look for it," he said.
So far, the spread of white sweet clover has been limited mostly toroadsides and disturbed areas, such as construction sites. The weedflourishes in gravel, or what agronomist researcher Steve Seefeldtwith the U.S. Department of Agriculture in Fairbanks called "basicsoil."
"Once it gets off the road bed it's dealing with more of an acidsoil," he said. "Once it gets to acid soil and can't make its ownnitrogens, it sort of loses its advantages."
While white sweet clover extends for more than 150 miles on theHaul Road, the weed-pulling effort has been concentrated at rivercrossings
In addition to pulling weeds, this year workers experimented byusing weed whackers to remove and inhibit first-year growth.Another option that has yet to be tried is re-seeding areas withmore aggressive native grasses to out-compete the weeds.
A two-week, weed-pulling campaign each year, though, isn't going tobe enough to prevent the spread of white sweet clover, Gronquistacknowledged. As she drove along the highway on Tuesday, Gronquistpointed out mature plant after mature plant.
"There's a second-year plant," she said, passing a four-foot-highflowering plant. "If we don't pull that one, then next year therewill 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 BrooksRange to pull white sweet clover along the Dalton Highway. Siegelis the volunteer coordinator for the Homer-based Friends of AlaskaNational Wildlife Refuges.
"It's become a mission for me now," Siegel said, crawling aroundnear Prospect Creek searching for young plants on a cold, soggy dayin the Brooks Range.
Siegel, a 68-year-old retired social worker who moved to Homer fromSan Diego three years ago, said programs like the weed-pullingeffort allow volunteers to see different parts of the state whilecontributing to a good environmental cause. The BLM pays forvolunteers' 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 fishbiologist from Homer, joined the weed-pulling crew on the DaltonHighway. Balland, 56, is hopeful he and the others can make adifference.
"It's something to be very concerned about," he said. "Any of theseinvasive plants have the potential of totally changing thelandscape as we know it, both flora and fauna."
Last year, a team of about a dozen volunteers filled plasticgarbage bags with 3 1/2 tons of white sweet clover, which was thenburned.
After three years of weed pulling, Siegel is optimistic thatvolunteers are having an impact.
"I was down on my hands and knees redoing an area that I did amonth ago and there were so many fewer plants and they're prettysmall," she said.
Gronquist, too, thinks the weed pulling has made a difference, atleast in the areas around the river crossings.
"We can't eradicate it but we can contain it and almost eradicateit at river crossings," she said. "We've been able to inhibit newgrowth."
Seeking a solution
Even with all the volunteers in the world pulling up white sweetclover plants along the Dalton Highway, it would be practicallyimpossible to stop the spread of the invasive weed, said Seefeldt,the researcher from the USDA.
"Eradication is a pipe dream" without using herbicides, Seefeldtsaid.
Part of the problem with pulling mature plants is that it disturbsthe ground and distributes more seeds to grow. Seeds can live forup 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 tosee what works against white sweet clover and what impacts it mighthave on other plants and animals.
"There are some herbicides that we found that provide excellentcontrol 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 youspray it and it stays active for a long time, so any new seedlingsgerminating are killed."
However, it will kill some native plants, Seefeldt acknowledged.
Scientists are hoping to see if moose will eat white sweet cloverthis fall at the Kenai Moose Research Center and determine whetheror not moose pass the seeds through their digestive systems,Seefeldt said.
Scientists also are studying whether white sweet clover willcolonize burn areas, of which there are several along the DaltonHighway and in the Kanuti refuge. So far, there has been noevidence the weed is sprouting up in burned areas.
The BLM is in the process of conducting an environmental assessmentof the impact white sweet clover is having and composing amanagement 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 andInvasive Plants Management.
But both Spindler and Gronquist said something will eventually haveto be done to stop the spread of white sweet clover and otherinvasive species.
"I think eventually the public will understand we have to useherbicides," Spindler said. "The question I have is how can we usethem safely near water?
"If we can hold them at bay until we get the necessary researchdone, maybe we have a chance," he said.