Researcher Discovers Solution For Invasive Tree

In Nevada, saltcedar trees have taken over many of the state’s streambanks and lakeshores, according to Tom Dudley, associate research professor at the university’s Department of Natural Resources and Environmental Science. Sucking up large amounts of precious water, saltcedar (or tamarisk) trees were originally brought to the U.S. for use as ornamental plants and soil stabilization.

“When the beetle eats as little as 5 percent of a saltcedar, the remaining foliage dries up, causing as much as 100 percent defoliation and ultimately killing the tree,” Dudley said. He added that he and his research colleagues believe that the saltcedar is at least partially to blame for lack of adequate water flowing into Nevada’s Walker Lake, near Hawthorne.

According to the Department of Agriculture’s Jeff Knight, one of the university’s partners on this project, “this has been one of the most successful biocontrol projects in all my 25 years in entomology in Nevada. It has had a dramatic impact on the ecosystems in Nevada agriculture, water levels, wildlife and riparian bird habitats.”

Unlike the bark beetles plaguing trees in the Lake Tahoe basin, this leaf-eating beetle -- about the size of a ladybug -- was purposely released into strategic areas across Nevada with hope that it will ultimately kill the invasive saltcedar tree.

The Nevada Division of Wildlife controls saltcedar with herbicides because the tree competes with native vegetation and provides poor habitat for wildlife. However, the beetle has proven to be a promising alternative and is the first USDA-approved biological control agent for saltcedar in the United States.

“This biological control agent offers a new tool for controlling non-indigenous species in an area,” said Knight. “Biocontrol will never eliminate saltcedar, but it can be a major component of integrated pest management, reducing the amount of pesticides and other forms of pest control used.”

Dudley added that it takes repeat defoliations to actually cause tree mortality, but significant progress has been made.

“We anticipate that we will see dead trees this year after three years of defoliation,” he said. “In 2002, we saw four acres of saltcedar that were defoliated. This year, we have about 1,000 acres -- a phenomenal increase.”

Dudley expects 3,000 acres could be affected by the end of the year, and said the research team also “has noticed an increase in some wildlife species, such as riparian birds and small mammals that like to eat the beetles.”

The USDA Agricultural Research Service, which is overseeing the project, is very aware of the potential for side effects when releasing new species into the environment, Dudley added. Therefore, the university’s initial research, which began collaboratively with Knight in 1997, was conducted in specially designed beetle cages. The beetles weren’t openly released in Nevada until 2001.

The biocontrol research is being conducted at three Nevada sites: on private land at the Humboldt Sink; at the Stillwater National Wildlife Refuge; and at the Walker River Paiute Reservation. There also are plans to initiate a new site this year on Pyramid Lake Paiute land along the lower Truckee River, Dudley said.

Nevada is one of eight states where the research is conducted under the “Saltcedar Biological Control Consortium,” a multi-agency and multi-partner effort that includes private interests like the Cattlemen's Association and conservation groups such as The Nature Conservancy.