Taking out tamarisk
Asian beetle becomes ally in the fight against noxious tree

Volunteers with the Tamarisk Coalition track the spread of the tamarisk leaf beetle on the Colorado River outside of Grand Junction. The beetles are proving to be a strong resource in the fight to stop the spread of the invasive trees./Photo courtesy of the Tamarisk Coalition

by Will Sands

An unwelcome visitor’s attempt to take over the rivers throughout the Southwest is not going unchecked. Tamarisk, the “poster child” for non-native plants, is continuing to squeeze out native species and exhaust scarce water resources throughout the region. But there is also a new ally in the fight against the noxious weed’s spread – a small beetle from Central Asia.

Tamarisk, or salt cedar, is a native of Eurasia introduced to North America by nurseries that sold the small tree as an attractive, quick-growing ornamental. However, without any natural predators, the trees spread rampantly from front yards into river corridors and beyond. Since its first introduction, the tenacious plant has seeded itself all over the West, displacing more than 1.6 million acres of willows, cottonwoods and other native vegetation. It is also estimated that each year the thirsty trees consume 2 to 4.5 million acre-feet of water from Western rivers, water that could meet the needs of 20 million people or 1 million acres of irrigated farmland. Tamarisk also recently set deeps roots in the Animas River drainage, joining Russian olive and Siberian elm, two invasive trees that have been on the local landscape for many years.

“The big issue is the drought in the West,” said Tim Carlson, executive director of the Grand Junction-based Tamarisk Coalition. “Tamarisk has a well-deserved reputation for being thirsty, and the concern is that as it spreads, it uses more of that valuable water.”

But now a decades-old effort to bring a natural tamarisk predator into the region is beginning to yield strong results. Tamarisk stands along the Dolores, Colorado and San Juan rivers have taken hard hits in recent years thanks largely to the release of a non-descript green bug known as the tamarisk leaf beetle.

In conjunction with the U.S. Department of Agriculture, Dan Bean, of the Palisade Insectary, first explored bio-control of tamarisk in 1987. At that time, Bean discovered Diorhabda elongata deserticola Chen, a beetle native to China and Kazakhstan that subsists exclusively on the invasive tree. A decade of study went into the beetle. When land managers were confident the bug would feed only on tamarisk, it was approved for open release in 2001. Initial test releases of the bugs were conducted in Delta, Utah, and central Nevada, where hundreds of acres of tamarisk were rapidly defoliated by the bugs. In 2004, beetles from Delta where transported to Moab and Horsethief bench outside of Fruita. Not only have those local transplants thrived at the expense of tamarisk, they have started to spread through the region and chewed through many of the invasive trees in their wake.

“The beetles in Moab and in Horsethief Canyon have taken off,” Bean said. “In 2008, they blasted their way up the Dolores River and are past Bedrock and have reached as high as McPhee Reservoir. They’ve also started to sweep across from Monticello and down into the Cortez area.”

Beyond having a huge appetite for tamarisk leaves, the tiny beetles are well suited to the Southwest, which is similar in latitude to their native range in Asia. Further south or north, introduction efforts have been hampered by poor reproduction by the bugs.

“Regionally, the effort has exceeded expectations,” Bean said. “We expected that the beetles would present a mild challenge to tamarisk and open the way for some natives to return. We didn’t realize that we’d see complete defoliation of large stands of tamarisk.”

A jar of tamarisk leaf beetles is released a large stand of the invasive trees. Utah land managers have embraced bio-control of tamarisk with open arms. Colorado, on the other hand, is taking a more cautious approach to releasing the beetles./Photo by Brian Swedhin

Carlson agreed, noting that the beetle has become a major prong in the fight against the invasive trees. “The beetle is going to be a really important tool in solving the tamarisk problem,” he said. “It’s certainly a cost-effective way of eliminating a lot of trees.”

Central to the tamarisk beetle effort is Fort Lewis College graduate and Durango resident Levi Jamison. Jamison serves as a biological/mapping technician and has been tracking the beetles’ spread through Utah and Colorado for several years.

“The larva come out, start eating the leaves, and they just hammer the trees,” Jamison said. “But the trees do re-foliate in winter and it takes at least four years to completely kill the trees.”

Bio-control requires more time and is less effective than mechanical or chemical treatments, said Jamison. However, it is the most financially viable alternative to taming the “scourge of the West.”

“Economically, it’s a much more viable option,” he said. “There’s no way the federal government could ever treat all of the tamarisk by conventional means. Ultimately, a combination of bio-control and mechanical and chemical treatment will be the way to solve this problem.”

However, there are some concerns that this biological solution could cause some problems of its own. The U.S. Fish and Wildlife Service has objected to releases of the beetles in the Animas River drainage because of the endangered southwest willow flycatcher. In an ironic twist, the flycatcher nests in tamarisk when the native willow has been displaced. However, Bean doubts the validity of this claim.

“There’s no evidence at all that the beetles harm the birds,” he said. “In fact, there is evidence that they provide an additional food source. The concern is that without willows or tamarisk, the birds will have no nesting sites.”

Bean also disputed any danger of the beetles making a host jump and developing a taste for native plants. He noted that no species are even remotely similar to tamarisk, and when the beetles are finished with a stand they virtually disappear.

“They leave the area when the plants are defoliated,” Bean said. “They get up in the wind and they’re gone. I always tell people that this is a bug that would rather commit suicide than switch hosts.”

Killing stands of tamarisk does open the door to other noxious weeds, and tamarisk, whether its alive or dead, poses major fire risks. However, for Carlson and Bean, all of these issues are secondary ones.

“My top concern is if people start believing that beetles are going to single-handedly solve this problem,” Carlson said. “Controlling tamarisk requires a variety of approaches. There is just no silver bullet when it comes to eliminating these trees.” •