Borrego Sun - Since 1949

Beetles: Answer to Invasive Trees

 

Last updated 7/18/2023 at 12:20pm

Ernie Cowan

Tamarisk beetle at Middle Willows in Coyote Canyon

A decades-old effort to kill invasive tamarisk trees in Anza-Borrego may be getting help from Mother Nature in the form of a beetle that naturally destroys the plants.

Resource managers and environmental watchdogs are excited by the arrival of a tiny insect known as the tamarisk beetle that may accomplish what expensive mechanical controls and herbicides have done with only limited success.

The announcement came from RiversEdge West, an organization dedicated to restoring riparian ecosystems.

Part of that effort is to produce an annual tamarisk beetle distribution map, showing how populations of the insect are expanding.

Many desert lovers are surprised to learn that tamarisk trees, also known as saltcedar, are invasive, non-native and thirsty plants that consume much of the limited water supply in arid places. The result is a decline in native plant, bird and insect species.

Thick stands of invasive tamarisk disrupt native plant communities by monopolizing limited sources of water which also degrades wildlife habitat.

For decades, Anza-Borrego Desert State Park has been engaged in efforts to remove the invasive trees through mechanical clearing efforts and topical herbicides.

Former Park Superintendent Mark Jorgensen said he has now found beetles in local tamarisk trees.

"This could be an interesting story, since folks will be noticing the effects and talking about it," he said.

Apparently, the tamarisk killers have slowly migrated from Utah.

"The beetle was studied by USDA in the Old World for years as a pest which fed on tamarisk. After testing to make sure the beetle didn't feed on natives or agricultural species it was introduced in Moab, Utah and Big Bend, Texas to control tamarisk," Jorgensen said.

Four species of tamarisk beetles are found in regions of China, Kazakhstan, Uzbekistan, Greece and Tunisia where there are native stands of the trees.

Tamarisk beetles were introduced in the United States in 2001 and have now become an important biological control agent that specifically targets tamarisk trees.

Now, according to RiversEdge, a concentration of the beetles in tamarisk trees along the Colorado River are spreading into Borrego Springs.

Rows of tamarisk trees in the northern part of Borrego Valley are already being killed by the beetle infestation.

"The easiest trees to observe are just along Palm Canyon Drive across the street and east of J&T's tire shop," Jorgensen said.

Jorgensen has also found the beetles on private property in Borrego Valley and at a local resort.

Scot Martin, a retired park resource manager who headed up the Tamarisk eradication team, has also found them at Middle Willows in Coyote Canyon, and Sicco Rood from the Steele Burnand Anza-Borrego Desert Research Center has also spotted the beetles.

"It's impressive that they spread around so fast. I confirmed the beetles all around the valley two weeks ago from the Sink to Borrego Palm Canyon and also at Tamarisk Grove," Rood said.

According to RiversEdge, it takes about three seasons for beetles to finally kill a tamarisk tree and have been successful with a kill rate of about 80 percent.

"We've spent hundreds of thousands of dollars and thousands of person hours trying to control tamarisk in more than 150 miles of drainages in Anza-Borrego since 1972," Jorgensen said. "This beetle will make a huge difference to the native riparian habitats in the park.

That money and effort was spent to control tamarisk in every major watershed from Carrizo Creek in the south to Horse Canyon in upper Coyote Canyon.

"This beetle may be a major factor in controlling resprouts and the new establishment of tamarisk in treated canyons.," Jorgensen said.

He speculates the insects arrived in Borrego from winds that pushed them west from established populations along the Colorado River.

If you'd like to keep an eye out for tamarisk beetles, look for a bug about the size of a ladybug, with a thinner body. They are described as greenish to straw-colored with darker brown stripes running along their back.

Tamarisk beetles and their larvae control the invasive trees by feeding on their leaves. This defoliation leaves the trees dry and brown and weakens them and reduces their ability to spread.

 
 
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