South Platte – Here come the beetles.
The U.S. Forest Service on Thursday deployed a special weapon against a tough weed that has infested portions of the Pike National Forest southwest of Denver.
In a rocky canyon bottom carved by the South Platte River, biologists unleashed a quarter- million tiny flea beetles to dine on clusters of leafy spurge that have infiltrated the Buffalo Creek burn. Other releases will turn hundreds of thousands more beetles loose on the weed in other areas of the forest.
The beetle offensive is part of a concerted war against leafy spurge, one of the most rapacious invasive plants in the West.
The weed has taken over almost 3 million acres, costs ranchers up to $45 million a year, and has been a bane to wildlife and native plants.
Leafy spurge flea beetles, named for their favorite food and their jumping ability, dine on the weed both as larvae and adults. In large patches of spurge, beetle populations can overwhelm the weed, opening a toehold for native plants such as willows.
“We’re looking to inundate some of these patches,” said South Platte Ranger District biologist Denny Bohon, who estimates there are 1,000 acres of spurge in her district.
Thursday’s release was the largest in the Pike National Forest.
Bohon, her clothes flecked by tiny jumping black dots, said spurge has colonized sandy riverbanks scoured by floods that tore through the valley after the Buffalo Creek fire of 1996.
The spurge wars have been fought with weapons such as herbicides and fire over the past 50 years. Most have been costly and ineffective.
Along the South Platte, the proximity of the spurge clumps to the river, Denver’s main source of drinking water, made the use of chemicals risky. Treating the riverbanks and rugged slopes of the burn area with chemicals could cost up to $175 per acre, Bohon said.
The bugs, on the other hand, were free. About half a million were collected in three hours by butterfly net near Cherry Creek State Park in Arapahoe County within the past few days.
Only about one-third of the released beetles are likely to survive, said Jonathan Rife, Douglas County’s weed inspector. But over time, the bugs are expected to nibble many patches of spurge to death.
First identified in the West in North Dakota in 1909, leafy spurge has doubled its acreage every 10 years. The European invader had a 100-year head start before control measures started.
The root system of the 3-foot-tall plant can reach more than 40 feet, giving it the ability to recover quickly from mowing and herbicides.
Flea beetle larvae munch on the weed’s fine roots, reducing its ability to absorb nutrients. Adult beetles eat spurge leaves and its yellow-green flowers.
Extensive testing has shown the flea beetles, also from Europe, don’t have a taste for North American plants. Research in Montana, the Dakotas and Canada shows beetles can reduce spurge density by 90 percent over time.
And unlike chemicals, flea beetles and other biological controls don’t have to be reapplied year after year.
“That’s the beauty of bio-controls,” said Dave Kazmer, an entomologist with the Northern Plains Research Laboratory in Sidney, Mont. “When it is successful, it is a self-sustaining population that replaces itself year after year.”
Using introduced bugs to combat alien plants dates to the late 1800s, but in the past two decades, bio-controls have become a critical tool in land managers’ arsenal, Kazmer said.
In the West, biologists are releasing another beetle species to control tamarisk. Other bugs have been enlisted to combat toadflax and knapweeds.
But bio-controls won’t work everywhere, experts say. A plant infestation has to be large enough to provide food for the insects. And extensive testing must be done to ensure the insects don’t turn on native plants.
Staff writer Theo Stein can be reached at 303-820-1657 or tstein@denverpost.com.
