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New Mexico State University

New Mexico State University

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Leaf Beetles Target Water-Gulping Salt Cedars

LAS CRUCES - A leaf beetle about the size of a pencil eraser could be the ax needed to bring down one of New Mexico's most formidable invasive tree species, the overly thirsty salt cedar, a New Mexico State University scientist said.

Dave Thompson, an entomologist with New Mexico State University, checks the area next to an experimental field cage used to evaluate control of salt cedar using leaf beetles. The tiny voracious bugs only eat salt cedar leaves. Extensive quarantine lab tests at NMSU indicate they are not a threat to the state's cash crops when released into open areas. (09/15/2003) (NMSU Agricultural Communications Photo by J. Victor Espinoza)

The beetles have a proven track record in defoliating the invasive trees in other states, and now researchers have begun a new study with them along the Pecos River.

"There are very few things that eat the leaves of a salt cedar tree, and these beetles are one of them," said Dave Thompson, an NMSU entomologist. "They'll literally eat all the green foliage off the tree." In one Nevada test earlier this year the beetles completely defoliated almost 400 acres from a 10-acre start in one season, he said.

Last month, about 600 of the leaf beetles were released along the Pecos River near Artesia. Initially, the beetles were held in a cage roughly the size of a small house, about 500 square feet. Tracking beetle populations and salt cedar inside and outside the field cage is a priority this fall and next summer.

"We're really interested in how they make it through the winter, and how they respond to the shorter day in the south," Thompson said. "So far, there hasn't been a release established south of Colorado." If all goes well at the Artesia location, releases will be made at two other sites farther downriver near Carlsbad later in the spring.

Using leaf beetles to help manage the salt cedar has been tested extensively in other states. The beetles have been released in California, Nevada, Utah, Colorado, Wyoming and Texas. Thompson, who is an associate professor in NMSU's entomology, plant pathology and weed science department, emphasized that beetle-based salt cedar control is not a quick fix.

"It could take years of defoliation to halt the spread of the trees," he said. "But the control has the potential to be permanent and self-sustaining."

And any concerns about the beetle moving beyond salt cedar to eat native plants are negligible. "If there is no salt cedar, these beetles will disappear," Thompson said.

As part of the research, NMSU researchers are studying four different subspecies of the beetle from four different regions. Originally, U.S. researchers solely relied on a beetle species from China. Now, NMSU scientists, working in cooperation with the U.S. Agricultural Research Service and the U.S. Bureau of Reclamation have added three new beetles from Crete, Tunisia and Uzbekistan, which should be better suited to the state's hot, arid conditions.

Releases along the salt cedar choked-Rio Grande await approval from state and federal environmental agencies. The main concern in releasing the beetles has been the endangered Southwest willow flycatcher, which is known to nest in salt cedar.

"We're hopeful that we'll be able to begin our research on the Rio Grande soon because it's a much better location in terms of native vegetation recovery," Thompson said. The permitting process for allowing the Rio Grande portion of the scientific study has been underway for five years.

The beetle eats only the salt cedar and is not a threat to other vegetation, Thompson said. In quarantine lab tests at NMSU and federal labs in California and Texas, leaf beetles were confined in small cages to determine whether they would feed and reproduce only on the troublesome tree.

NMSU's quarantine lab is one of about a dozen in the nation. Authorized by the U.S. Department of Agriculture, the lab tests nonnative insects and weeds to see how they affect the New Mexico environment.

There's plenty of work for the beetles to do along New Mexico's rivers. Thousands of acres of dense salt cedar thickets are choking many of the state's rivers, creating an unhealthy tangle of trees and brush that pose a high fire danger in addition to using increasingly scarce water.

Nonnative species like salt cedar are also crowding out the native cottonwoods and willows. The feathery, tough-to-kill salt cedar grows prolifically in poor, salty soils along riverbanks and is resistant to disease. And up until the discovery of the beetle's penchant for eating the tree's leaves, it had no effective natural enemies

In some areas salt cedars may consume up to 14 acre feet of water a year when the water table is near the surface, said Keith Duncan, a brush and weed specialist with NMSU's Agricultural Science Center at Artesia. A mature salt cedar can guzzle 200 gallons a day, he said.

Moreover, the trees are incredibly difficult to eliminate because they reproduce easily, Duncan said. One mature tree can produce as many as 500,000 seeds a year.

Salt cedars first were introduced into the United States in 1854 from the Middle East as ornamental windbreaks and soil stabilizers. The prolific, water-guzzling plants soon became invasive pests, drawing salt to the surface, killing native plants and growing in thick stands that became fire hazards.

As late as 1968, the fast-growing tree was planted along waterways in the Western states to help control erosion. Now, every Western state, except Washington is dealing with the trees' seemingly unquenchable thirst.