Leafy spurge hit by beetle bombs

Researchers launched a unique aerial assault this summer on a stubborn noxious weed that has vexed land managers for more than a century. Leafy spurge, a tenacious weed introduced from Eurasia in the mid-1800s, is aided in its propagation by mourning doves who ingest seed and deposit it in the form of waste. Left to their own creeping, leafy spurge plants can expand about 15 feet per year. With the aid of birds, however, its territory burgeons at a much faster rate.

Leafy spurge has no natural enemies in North America. All photos by Chad Cheyney.

With a taproot that extends more than 20 feet in depth, a shallow, horizontal root system that creeps steadily, plus aerial distribution by birds, leafy spurge has become a major concern and economic threat in most regions of Idaho. It has created significant economic losses in the Dakotas, Wyoming, and Montana, and threatens to do the same in Idaho. Unfortunately, the weed has no natural enemies in North America. A relatively new biological immigrant from Europe, however, appears to be highly successful in stifling the weed’s progress and reducing it to a manageable level.

Resource managers in other heavily impacted areas have turned to Aphthona flea beetles, originally imported from Europe and Asia, to limit the spread of leafy spurge. In their larval stage, the beetles thrive on the weed’s shallow root system. Adult flea beetles feed on spurge leaves and stems. They are considered to be a sustainable and inexpensive approach to controlling leafy spurge.

Acres of leafy spurge infestation in green (illustration on the right)

The most common way to distribute the voracious beetles–which limit their diet to leafy spurge and have little or no impact on other desired vegetation–was to spread them by hand. But the weed has become established on state and federal land that is difficult or impossible to reach. The conventional means of introducing flea beetles in those areas would be inefficient at best, ineffective at worst. Reaching those areas would require ingenuity.

That’s where Chad Cheyney, UI extension educator in Butte County, and Andrew Deutscher entered the picture. Deutscher, a noxious weed biologist, was working on a forest health protection project for the U.S. Forest Service in the Shade Creek Ranger District near Boise when he struck on an idea to create "bug bombs" and drop them from a helicopter. Aided by a $6,000 grant from the Idaho Department of Agriculture and multi-agency cooperation, this aerial counterattack was implemented in July under Cheyney’s direction.

Using flea beetles he collected the year before, Deutscher designed and created bombs from half-pint cardboard food containers. Holes were punched in each container and then covered with masking tape. A metal washer was added for weight and a streamer attached to aid the flight. Approximately 120 of the bombs were dropped from a helicopter on inaccessible or difficult to reach terrain in southern Idaho. The helicopter, already under contract for fire fighting, was diverted for about three hours at a cost of just $2,000.

Above: Flea beetles are separated from vegetable mater and other bugs. Then, 2000 beetles are placed in each food container "bomb" and dropped by helicopter.

"We wouldn’t have even come close to treating that much area in one summer," Cheyney said. The alternative, spot-spraying affected areas with herbicides on the ground, is much more costly at $150 to $250 per acre.

The grant from the Idaho Department of Agriculture also included video-

taping the aerial attack and producing an instructional tape to guide future public and private bug bombing operations.

On the surface, the spread of leafy spurge into Idaho was a depressing proposition, Cheyney said. Controlling the noxious weed appeared to be hopeless. "Everyone was pretty distressed for letting it happen," he said of the weed’s proliferation. "Now there’s something we can do about it, and we’re doing it together."

The cooperative effort also included the U.S. Forest Service, the U.S. Bureau of Land Management, weed and extension districts in Butte and Custer counties, and the National Park Service (Craters of the Moon National Monument). "There’s no doubt we’ll do this again," Cheyney added.

Left: Collecting flea beetles for leafy spurge control.

Although it may take another year– or perhaps longer–to judge the total effectiveness of the new beetle distribution method, researchers are optimistic about the results of the initial bug bomb effort. For information about using this biocontrol method to control leafy spurge or to inquire about the aerial attack, contact Cheyney at the University of Idaho Butte County Extension Office, PO Box 832, Arco, ID 83213-0832, ccheyney@uidaho.edu. See http://www.team.ars.usda.gov/ for more information on eradicating leafy spurge.

—Mel Coulter

Click here to see more photographs.

For more information on leafy spurge and other weeds, see Idaho's Noxious Weeds, available from Ag Publications, (208) 885-7982.