A new sort of land war is raging across Oregon. Invasive plants that landed like aliens from the outer spaces of Asia, Europe and South America are taking over entire ecosystems.
Many of them are pretty; some are poison to people and animals. Others crowd out crops or wildlife habitat. All share the same fatal flaw that has landed them officially on the list of 105 least-wanted plants in Oregon: they don’t grow well with others. With no natural enemies and few climatic or geographic controls, these plants can aggressively crowd out native flora, potentially unraveling the dense tapestry of plants and wildlife into the ecological equivalent of a parking lot.
Scotch broom, for example, was brought to the Pacific Northwest by early settlers homesick for the flowers of their native British Isles. Scotch broom rapidly spread into forests and woodlands throughout western Washington and Oregon, where it now occupies millions of acres.
“Some people may look at the golden hillsides resulting from Scotch broom and think it’s a pretty wildflower that belongs in Oregon,” said Tim Butler, supervisor of the Oregon Department of Agriculture’s Noxious Weed Program. That’s the farthest thing from the truth. Scotch broom costs the state about $47 million each year by its impact on natural resources, particularly on timber production.
“Controlling invasive weeds is a real white-hat issue,” said Steve Radosevich, an Oregon State University Extension Service weed ecologist who has 30 years of experience in weed research. Farmers, ranchers, environmentalists and landowners all form a united front against these invaders.
On a five-acre test plot in the former Camp Adair military base north of Corvallis, Radosevich and a research assistant have targeted one of the state’s thorniest and most aggressive agricultural runaways, Himalayan blackberry. They discovered that by mowing the crowns (the point where the canes join at the base), disking them up and raking them out, they have reclaimed much of the thicket. It is a simple, affordable treatment using standard farm equipment that has kept the blackberries at bay even three years later, according to Radosevich. Such controls target and exploit the plant’s weakness: remove the crowns, and you’ve knocked back the plant.
“The landowner could get goats or sheep in here the year after treatment to keep down the resprouting canes,” Radosevich said.
The war on weeds has led researchers to look for weaknesses in many of Oregon’s least-wanted invasive plants. A famous example is the successful control of tansy ragwort using its natural enemies imported from Europe. Peter McEvoy, an entomologist with OSU’s Department of Botany and Plant Pathology, helped spearhead the biological control of tansy ragwort 20 years ago. Now, he says, there are seventy insects and pathogens providing a measure of control on thirty different weeds.
“The public gets back about $15 in benefits for every dollar spent when a noxious weed is reunited with its natural enemy,” said ODA entomologist Eric Coombs, who was integral in helping to bring tansy ragwort under control.
Take, for example, purple loosestrife, whose thick stands clog waterways and reduce water quality, stream flow and habitat for waterfowl. The best hope for biological control of this European native lies with two leaf beetles, a root-feeding weevil and a seed capsule weevil. Since their introduction a few years ago, the insects have eaten their way through 90 to 95 percent of the purple loosestrife at the Baskett Slough National Wildlife Refuge west of Salem.
While the reduction of purple loosestrife is promising, McEvoy said it doesn’t necessarily mean an instant return of native vegetation and associated vitality. Reed canary grass — a noxious weed introduced to Oregon in the early 20th century — has spread into some areas where the loosestrife declined.
Weeds infest all parts of Oregon, from city parks to suburban backyards to crop fields and rangelands. Many of the beautiful invaders — purple loosestrife, Japanese knotweed, butterfly bush — began as garden specimens, imported for their beauty in the landscape.
The more the public recognizes that some pretty plants have ugly – noxious – habits, the better, said Jed Colquhoun, an OSU Extension weed specialist in the crop and soil science department. Recently, he has been speaking to public groups about the dangers of noxious weeds – sometimes with surprising results.
“I was giving a talk on noxious weeds and the audience was very surprised that some noxious weeds began their ‘careers’ as garden ornamentals,” he said. The group admired the beautiful small broomrape, loosestrife and even water hemlock. And who can blame them? What gardener doesn’t like a plant that establishes well, requires little care or fertilizer and grows almost anywhere? When does a gardener decide that a pretty, hardy perennial has become a problem?
And so it is with the rise and fall of lilac-like butterfly bush, Buddleja davidii. A few years ago, garden clubs and nature advocates touted the virtues of planting the pretty butterfly bush as a way of attracting … butterflies. That was before the native Chinese variety of Buddleja thickly infested the North Fork of the Willamette River near Oakridge and the Coquille River near the coast, spreading to almost every county in western Oregon and Washington.
Last year, the ODA added Buddleja to its list of class B noxious weeds, targeted for control everywhere in Oregon except peoples’ yards, where gardeners now can grow different horticultural varieties of butterfly bush. James Altland, a nursery crops researcher at OSU’s North Willamette Research and Extension Center in Aurora, and graduate assistant Julie Ream are investigating whether these cultivated varieties are better sharers of the land than their aggressive parent.
Not all introduced weeds came by invitation; many came as stowaways. Downy brome, commonly called cheatgrass, hitchhiked in from the Mediterranean a century ago and has since turned huge swaths of rangeland into single-species wastelands. The spread of downy brome is contributing to the loss of habitat for a threatened bird of the western range, the sage grouse.
Downy brome represents one of the biggest challenges to eastern Oregon farmers and ranchers, according to Corey Ransom, an OSU assistant professor in weed control research at the Malheur Experiment Station in Ontario. Although the grass provides some forage for grazing animals early in the season, the quality drops as the grass matures and the seedheads become sharp and irritating to tender mouth tissues. Cheatgrass is especially problematic in dryland fields of winter wheat, where its roots can extend three to four feet and greedily suck moisture from the soil. A severe cheatgrass infestation in winter wheat can lower grain yields by up to 90 percent.
Estimating the real-world cost of noxious weeds is a challenge, according to Carol Mallory-Smith, a weed biologist with Oregon’s Agricultural Experiment Station. Mallory-Smith studies herbicide resistance in weeds such as jointed goatgrass, which infests wheat fields in eastern Oregon. Winter wheat’s “evil twin,” jointed goatgrass is a clever mimic that grows in wheat fields, contaminating wheat in the Great Plains and Pacific Northwest and costing U.S. wheat farmers $45 million in losses each year. So farmers were keenly interested in an herbicide-resistant wheat variety that enabled herbicide treatment of fields that would target jointed goatgrass and would not harm the wheat. Unfortunately, jointed goatgrass and wheat can produce weedy hybrids with the potential to be herbicide resistant as well.
Increasingly, weed control in crops involves an integrated strategy that targets specific vulnerabilities of the weed.
Consider small broomrape, an exotic-looking flower stalk whose roots have been sucking the life out of the Willamette Valley’s seed industry, leaching nutrients from the root systems of red clover. Mallory-Smith explains the current control strategy, which involves chemical control and a bit of trickery. “We’re growing wheat as a ‘false host’ that will stimulate germination of weed seed, but does not allow the weed plant to develop. It reduces the seed in the soil over time.”
Landowners, weed ecologists and landscapers are working together to identify and control the noxious weeds in Oregon. A new Internet-based network, called WeedMapper, was developed by OSU and ODA scientists to allow rapid reporting of noxious weeds across the state.
Early detection and rapid response are critical in weed control. It was an ODA Noxious Weed program staffer who first detected the arrival of kudzu, the “scourge of the South,” outside of Portland. The carpet-like foliage of this sweet-smelling vine can advance 60 feet a year. Kudzu immediately made the state noxious weed “A” list as a kill-everywhere entry. Public involvement in finding a second site in 2000 and a third in 2001 has helped the ODA in its “search and remove” efforts to bring kudzu under control, for now.
In some Oregon cities, early intervention and public involvement already are proving effective. For example, volunteers with the Forest Park Ivy Removal Project in Portland descend every week on the park as a no-Ivy League to remove smothering English ivy, or that “botanical barbarian,” as they call it. Their motto: “Leave no vine behind.”
When it comes to noxious weeds in general, researchers are hoping similar sentiments regarding noxious weeds will take root — and spread.