When imported ornamental trees turn renegade, sometimes it takes an imported killer to chew them down to size.
Texas Cooperative Extension entomologists are using beetles from Crete, Greece, to combat invasive saltcedar along the Pecos River in West Texas.
Saltcedar was first introduced from southern Europe and Asia in the 1800s for erosion control and as an ornamental. Unfortunately, it was far too adaptable. Now thick stands of rogue trees choke many of the state's environmentally sensitive western waterways, sucking up water to the exclusion of native vegetation and municipalities.
To help combat the program, Dr. Allen Knutson, Extensi! on entomologist at Dallas, and Dr. Jack DeLoach, Agricultural Research Service scientist at Temple, in 2004 successfully established a small population of saltcedar leaf beetles along a creek near Big Spring.
Knutson said those beetles have since spread along five miles of the creek and defoliated 40 acres of saltcedar.
Last year, Extension organized the Saltcedar Biological Control Implementation Program to release more beetles at sites in the Upper Colorado River Watershed and along the Pecos River.
The goal is to establish new populations of beetles at additional sites and thus speed the rate of biological control, Knutson said.
Releases of beetles by Knutson's colleague Dr. Mark Muegge, Extension entomologist at Fort Stockton, at two sites on the Pecos River have been especially successful.
Beetles were released in mid-summer of 2006 and defoliated several trees before cold weather stopped them. Muegge said the adult beetles overwintered and began feedi! ng and reproducing in April. Populations at both Pecos River s! ites inc reased and dispersed during the summer.
By mid-October, beetles had defoliated more than 500 saltcedar trees across about 90 acres along the Pecos River,@ said Muegge. "The rapid success at these sites demonstrates the potential these beetles have for long-term suppression of saltcedar on the Pecos River.
The saltcedar leaf beetle eats the trees= leaves, Knutson said. Without leaves, the tree can not manufacture food. Once defoliated, the saltcedar regrows new leaves which are soon eaten by another generation of beetles. After repeated defoliation, the trees slowly starve to death.
"After four consecutive years of defoliation, trees at the original Big Spring site are starting to die," Knutson said."We think the same will happen on the Pecos River."
Muegge said most of the Pecos River saltcedar was killed by an aerial herbicide program conducted by the Pecos River Ecosystem Project during 1999-2005. However, he said some landowners did not give permission for he! rbicides to be applied to the saltcedar on their land, or efforts to contact the landowners were unsuccessful. An estimated 3,000 acres of unsprayed saltcedar remain in the Pecos River corridor.
"These islands of living saltcedar pose an imminent threat to re-infesting the Pecos through seed dispersal," Knutson said. "Trees defoliated by saltcedar leaf beetles produce very few blooms and, as a result, few if any seeds.
"Thus, while it may take four or five years of repeated defoliation by saltcedar beetles to kill a saltcedar tree, the lack of leaves due to the beetles' feeding creates stress on the tree which limits seed production and allows grasses and other desirable plants to grow where saltcedar once dominated."
The Biological Control Implementation Program plans to establish saltcedar leaf beetles at other sites in the Pecos River watershed in 2008.
Muegge said research by U.S. Department of Agriculture scientists demonstrated that the beetles feed and! reproduce only on saltcedars and do not pose a threat to any ! crop or native plant. Both adults and larvae feed on saltcedar leaves, but larvae eat more leaves.
Knutson said federal and state agencies, including the U.S. Fish and Wildlife Service, approved the release of the beetles in Texas.
The saltcedar biological control project on the Pecos River was conducted in cooperation with the Reeves County Water Improvement District #2 and the Pecos County Water Improvement District #3.
For more information contact Knutson, at 972-952-9222 or Muegge at 432-336-8585.