Enter the tamarisk leaf beetle
Two years before the Southeast Utah Riparian Partners (SURP) met, the Grand County weed supervisor released the tamarisk leaf beetle, imported from Fukang, China, on private land along the Colorado River. The beetles quietly began to multiply; by 2006, they were making a noticeable impact. That summer, the Skyline Cooperative Weed Management area had a statewide weed meeting in Moab to assess the beetle damage.
Because tamarisk is so difficult to remove with cutting and herbicides, biologists began searching for an agent to safely control their growth. APHIS (Animal and Plant Health Inspection Service) has been studying the beetle (Diorhabda Elongata) rigorously for 20 years. The beetle feeds only on tamarisk and, so far, it has shown no ability to cross over and eat other species. Reassured, the Grand County weed agent collected beetles from one of the study areas (Delta, Utah) and released them onto privately owned sites along the Colorado River, where they were not subject to legal restrictions. He also released beetles in larger numbers and greater frequencies than others, a strategy that has allowed the beetles to prosper.
An astonishing result
The first season, the beetles defoliated only a few tamarisks. After one year, 2 acres were defoliated. By the next year, the insect populations were established and tamarisk was totally defoliated (though not killed) on over 10 miles of the Colorado River.
Year three was like watching a brush fire “brown out” several miles of riverbank a week. Suddenly, the Colorado River corridor had been defoliated from Moab to near the Colorado state line and downstream 70 miles to the Green River. Those once-green tamarisks were turned into brown skeletons. Within a week, the 800-acre Matheson Wetland Preserve in Moab turned completely brown. It is breathtaking. It is also sobering.
This fourth year, because of a cooler spring, the beetles had a later start, and tamarisks were not defoliated until the end of June. But within a week or two, huge strips along the river turned brown. Perhaps most promisingly, tamarisks have started dying out in the area where the beetles were first introduced.
Last fall the beetles went into diapause, a form of dormancy. Very quickly the tamarisk shot out new leaves, although certainly fewer than before. It was astonishing. This pattern will continue for a few years, until the root gradually weakens and the tamarisk die.