Lassoing wicked weeds of the West

Agricultural Research, July, 2007 by Marcia Wood, Alfredo Flores, Laura McGinnis, Erin Peabody

The Wild West.

It's an apt term when you consider how many leafy, exotic "outlaws" are overrunning pastures, hills, and valleys west of the Mississippi.

But ARS scientists and others are giving chase, pitting their knowledge and sustainable, science-based strategies against invasive weeds to stop their spread.

One of the most aggressive of these intruders is leafy spurge. This lanky perennial, actually a distant cousin of the poinsettia, made its way here from Europe and Asia. The yellow-flowered weed has doubled in acreage every 10 years since the early 1900s. It now infests over 5 million acres in 35 states and Canada, costing land managers around $144 million a year in control costs and other losses.

With the ambitious goal of cutting off--or at least slowing--spurge's relentless march across the Great Plains, ARS scientists at the Northern Plains Agricultural Research Laboratory in Sidney, Montana, formed "The Ecological Areawide Management of Leafy Spurge Program," or "TEAM Leafy Spurge" for short. Over 6 years, this cooperative, multiagency effort proved to many in the region--and elsewhere--that biologically sound tactics can make a significant dent in spurge populations.

Their most convincing accomplice in this "purge-the-spurge" endeavor?

A tiny beetle.

Miniscule, Yet Mighty

It may be slight--less than one-half-inch long--yet the flea beetle, genus Aphthona, could be a rancher's best weapon against spurge. This insect gets its "flea beetle" moniker from its tendency to briskly hop about. Unlike its namesake, however, it doesn't bother people, pets, or livestock.

The beetle has a well-honed taste for spurge, having been associated with the plant for thousands of years. That's according to David J. Kazmer, an ARS entomologist at Sidney involved in TEAM Leafy Spurge.

Flea beetles provide a powerful, two-pronged attack, says Kazmer. Adults nibble away on the plant's leaves and bracts, while their translucent, grublike larvae chew their way through the roots--a "direct hit to the plant's food reserves," Kazmer notes.

Aphthona beetles have reduced leafy spurge canopy cover and stem densities by as much as 95 percent at sites where they've been turned loose. Ranchers and landowners got to see the insects' impact with their own eyes during field tours and other popular TEAM Leafy Spurge events.

ARS scientists working in the United States and Europe began searching for natural enemies of spurge more than 20 years ago. Their studies revealed Aphthona's aptitude for stopping spurge and later confirmed that it feeds only on leafy spurge and does not pose a threat to crops or garden plants.

TEAM Leafy Spurge has logged some impressive stats. An estimated 45 million beetles were put to work over the length of the project. Many of those were given to landowners.

Beetles--or another spurge-suppressor, sheep--knocked back leafy spurge by 90 to 100 percent at the program's four main research and demonstration sites in North Dakota, South Dakota, Montana, and Wyoming. Plus, thanks to ambitious tech-transfer efforts, a core group of ranchers and land managers is now using beetles, sheep, or both to tame leafy spurge.

There's more. Herbicide use is expected to be reduced by at least 768,000 pounds in the 4-state project area by 2008. Within the same period, increasingly healthy grasslands are expected to support an additional $1 million in livestock production.

The project, especially its efforts to reach out to and educate landowners, is largely regarded as a great success. But scientists--including Kazmer--aren't finished yet.

"We're looking at enhancing our biological control strategies by using synthetic versions of the pheromones the beetles emit when hundreds of them cluster in one spot," he says. Releasing such compounds into the air might entice the beetles to expanses of spurge that have yet to feel their bite.

Squelching Saltcedar

Meanwhile, another diminutive beetle is sating its appetite on the leaves and twig bark of another aggravating weed--saltcedar. Though attractive and graceful, this tree is an unwanted invader of streamsides and riverbanks throughout much of the West. But the brown-and-yellow, nearly quarter-inch-long Diorhabda elongata beetle now has a solid track record of tackling saltcedar, also known as "tamarisk."

Native to a region stretching from Asia to the Mediterranean, saltcedar was brought to America for the best of reasons: To stabilize soil. Today, it is shunned as a troublemaker in more than 20 states--from Wyoming south to Texas and west to California. It crowds out native species like willows and cottonwoods and creates impenetrable thickets that block livestock and wildlife--as well as rafters and canoeists--from reaching water. Where this renegade sheds its salt-rich foliage, other plants can't thrive.

ARS's interest in stopping saltcedar dates back to the 1970s and more recently took shape in extensive federal, tribal, state, and university collaborations coordinated through the Saltcedar Biological Control Consortium. As in the assault on spurge, the beetle recruited to whip saltcedar has won center stage and is now feasting on the plant in several western states. More states are waiting for the permissions needed to put the beetle to work.