Conjure up the lonesome sound of a harmonica in a dusty Western town where gunmen with jingling spurs reach for their six-shooters at high noon. The scene would be incomplete without a few tumbleweeds rolling past. But here's the truth: Tumbleweed doesn't belong on the Western plains.
An exotic also known as Russian thistle, it was accidentally imported to the United States from Russia 140 years ago in a shipment of flax seeds. Tumbleweed has since spread across 100 million acres, mostly in the arid Western states, where it displaces crops and native plants, triggers allergies, spreads wildfire, dries out soil and smacks into vehicles when it blows across highways.
Westerners know as well as anyone the damage that invasive weeds can wreak on crops and rangeland. Exotic plants out-compete natives and commercial crops because they sprout earlier in the spring, spread quicker, thrive on wildfire and withstand drought - and they end up costing the American economy an estimated $34 billion per year.
Tumbleweeds cause a unique set of problems. When they break off from their roots and tumble, they pile up against buildings and fences, creating a fire hazard. The plants can also be tricky to deal with not only because they can be huge -- some wouldn't fit in a typical dumpster -- but also because they're covered with thorns that cause painful, weltering scratches. Once the weeds get established, even the most vigorous attempts to cut, poison, burn or dig them up rarely halt their spread.
But help is on the way - maybe. Dana Berner and Bill Bruckart, researchers at the U.S. Department of Agriculture research center in Maryland, are studying pathogens that offer promise for suppressing the invasive tumblers.
Bio-control, which usually involves introducing a natural predator, has been tried before using insects. In the 1970s, two species of moths that bore into tumbleweed stems were released, but they failed to thrive or suppress the weeds. Introducing infectious agents for bio-control is less common: Just three foreign pathogens have ever been released to fight invasive plants in the United States. Once again, their success was limited, but researchers have higher hopes for the tumbleweed pathogens.
Thirteen years ago, Berner and Bruckart traveled to tumbleweed's homelands in Greece, Turkey and Russia to search for diseases that evolved with the plants. They brought several blight-causing fungi back to their lab and over the years have been testing whether they risk infecting any of the more than 60 other species of plants that share habitat with tumbleweed on this continent. Two passed the tests: A rust that makes the plant's leaves shrivel and drop off and another fungus -- known as CGS for its long scientific name -- that causes cankers on tumbleweed stems. The researchers have determined the fungi are host-specific and pose no threat to other species. They also conducted field studies in the country of origin, comparing plots of healthy tumbleweed with infected plots. In one such study in Greece, CGS killed nearly 100 percent of tumbleweed in a plot over two years.
"We can predict safety quite well," says Bruckart. "Efficacy is hard to predict, but we have high confidence in the safety of the organism."
Their confidence is not necessarily shared by USDA's Animal and Plant Health Inspection Service. Despite the years of testing and evidence in favor of the release, federal regulators have been hesitant to authorize application of the pathogens unless they're convinced the control is crucially needed. The researchers hope public dislike of tumbleweed will bolster their case and influence regulators to allow release of the pathogens.
If the pathogens are released, researchers expect them to spread from plant to plant on their own, saving the time and expense of applying pesticides to fight tumbleweed. The pathogen won't wipe out tumbleweed all together, but should suppress its growth, making it less invasive.
Controlling the weed would "increase the productivity and utility of millions of acres in the western U.S.," wrote USDA researcher Lincoln Smith in a 2008 paper. Berner adds, "The CGS would be a breakthrough, I'm convinced ... a darn good pathogen to control tumbleweed."
Controlling tumbleweed is one thing; controlling its admirers may prove harder. Some home décor enthusiasts coveting an old-time ambiance have been known to pay more than $80 to order dried tumbleweeds by mail. In its campaign to "Save the Great Western Tumbleweed," one online company promises to protect tumbleweeds "for many generations to come. For every dollar donated, Curious Country Creations will spread seeds so that tumbleweeds can continue with the history of the West."
So even if scientists get the go-ahead to begin the formidable task of controlling tumbleweed with pathogens, this pesky plant is bound to survive. Like guns, guts, cowboy hats and glory, tumbleweeds have rolled their way into our region's mythology.
Emilene Ostlind is a contributor to Writers on the Range, a service of High Country News in Paonia, Colorado (hcn.org), where she is the magazine's editorial fellow.