Old World enemies

South Dakota is joining the ranks of states that employ the bantam-weight Diorhabda beetle to help control spread of the saltcedar tree, one of the top three invasive species on USDA's most unwanted list.

South Dakota is joining the ranks of states that employ the bantam-weight Diorhabda beetle to help control spread of the saltcedar tree, one of the top three invasive species on USDA's most unwanted list.

The saltcedar, or tamarisk, originally was imported into the United States as an ornamental shrub in the early 1800s. Since then, it has aggressively spread, choking out native species along waterways throughout states in the Southwest and West. Claims have been made that the tree is drinking so much water that it actually is drying up rivers. The tree is known to leech salts out of the soil and secrete them from its leaves, depositing them in crystalline form on the ground, effectively preventing germination of other plants.

A secondary effect of saltcedar invasion is related to increased frequency of fire in affected areas, according to Jeffrey E. Lovich of the National Biological Service in Southern California. The drought-resistant nature of salt-

cedar contributes to a heavy "fuel load" in infested areas during drought. At the same time, its ability to survive fire, coupled with the fire intolerance of many native shrubs, effectively leads to saltcedar dominance in native plant communities in relatively short order.

It also interferes with peoples' ability to enjoy the outdoors, according to a study released by Craig Reed, an administrator with USDA's Animal and Plant Health Inspection Service. It states that dense stands of the weed interfere with camping, hiking and picnicking and extract up to 5 feet of water annually, while rodent density, bird density and bird species diversity are lower in riparian saltcedar infestations then in native ecosystems.


"Saltcedar has poor value as a forage plant for livestock and causes flooding, either by blocking channels directly or by increasing the deposition of silt," it states.

South Dakota responds

In just two years, saltcedar has expanded its territory in South Dakota from 5,000 to 6,500 acres, now occupying riparian habitats in 26 counties.

"I'd say it's a concern a major concern," says Mike Stenson, a weed management technician with the South Dakota Department of Agriculture. "If we ignore it, it will be a major problem."

A mature plant can produce 600,000 seeds, which can be carried by the wind and water. The seeds can germinate while afloat in rivers and streams and put down roots once they make shore.

The South Dakota Ag Department has found saltcedar in every major drainage in the western part of the state, "and we're starting to see it more in eastern South Dakota, popping up around the cattail sloughs, which is kind of discouraging for us," he says. "We are seeing it pretty much everywhere we look."

In May 2004, by emergency declaration, the South Dakota Weed and Pest Control Commission and South Dakota Secretary of Agriculture Larry Gabriel placed saltcedar on the state's noxious weed list. This required that for the following 180 days, any landowner with an infestation of saltcedar had to attempt to "prevent or limit the growth, spread, or development of saltcedar."

In North Dakota, saltcedar was discovered in 2001 along the Yellowstone River in McKenzie County. Since then, other populations have been found in all of the counties bordering Lake Sakakawea, as well as in Slope, Billings, Morton, Ransom and Sargent counties. It is in nine Montana counties and recently has been identified in northwest Minnesota.


The Diorhabda beetleTo battle the plant, scientists scoured its native lands in Eastern Europe and Asia, looking for its natural enemies.

"Saltcedar is an 'Old World' plant with no close native relatives here, but more than 200 natural enemies of saltcedar have been found in China and the former Soviet Union," Agricultural Research Service entomologist Raymond I. Carruthers says. "Insects like the Diorhabda beetle feed exclusively on saltcedar, making them ideal for biological control."

Observations made overseas by entomologists from many different countries confirm this. Diorhabda beetles keep saltcedar in check naturally in China, and it's hoped the insects can do the same in South Dakota, Stenson says.

"That's the way all biological control works," he says. "We have invasive species from other places, and they don't have any of their natural predators. Basically, scientists go back to the home range, find a predator and bring it over here."

After the yellow-striped, quarter-inch long beetles were brought to the United States, they were maintained in USDA quarantine laboratories in Texas and California, where they were subjected to extensive host range testing.

The beetles were offered a wide selection of native plants and crop plants, either in combination with saltcedar or exclusively. They preferred saltcedar to native plants and, in most cases, wouldn't feed at all on nontarget plants, choosing instead to starve while in search of a saltcedar plant. Since then, field tests have shown that when the insects finish feeding on saltcedar they do not move over to the nearest plant, but fly or crawl off in search of more saltcedar.

The beetle is the first approved by USDA as biological control agent for saltcedar in the United States.

Track recordDr. Dale Devitt, a University of Nevada professor of soil and water based in Las Vegas, notes that if, through removal or defoliation of saltcedar, the trees' water consumption could be reduced by half, enough water to supply water from nearby Lake Mead to an extra 125,000 people.


Allen Brinkerhoff, a grower in Pershing County, Nev., says he is thrilled by the results the beetles have had on the saltcedar infesting his land.

"They have done a good job," he says. "The effect is amazing."

The beetles defoliated 25 to 30 acres of his land the first year and two years later had cleared more than 1,000 acres.

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