Two such weeds, leafy spurge and saltcedar, are major economic problems in a number of states.
Leafy spurge is an aggressive invader that can squeeze out native vegetation. Annual losses due to reduced forage for livestock and wildlife range from $2.6 million in Wyoming to $76.3 million in North Dakota. Recreational and ecological losses may be even greater.
The weeds can severly irritate the mouths and digestive tracts of cattle, sometimes causing death. The plants' seed pods explode when dry, often projecting seeds as far as 15 feet. These seeds can live in the soil for up to eight years before germinating.
Leafy spurge can spread quickly. For example, in North Dakota, an estimate 20,000 acres were affected in 1962, 40,000 acres in 1973, 86,500 acres in 1982, and nearly 1.2 million in 1990.
Help may be on the way, however. Recent studies have found that Aphthona flea beetles feed on leafy spurge, removing more than 90 percent of plant mass within a 30-square-yard area around their release sites. The beetles aready have been introduced into areas with leafy spurge in Montana, Wyoming, New Mexico and the Dakotas.
Other projects seek biological control agents for saltcedar. The trees, which can grow up to 30 feet tall, infest more than one million acres along rivers and streams throughout the West.
Saltcedar was brought into the U.S. in the 1930s to protect streambanks from erosion. But, without natural enemies, saltcedar can crowd out plants crucial to wildlife. The trees also degrade wildlife habitat by increasing soil salinity, changing streamflows and increasing wildfire frequencies, according to the U.S. Department of Agriculture.
To battle this aggressive weed, the U.S.D.A. will soon place about 3,000 eggs of Chinese leaf beetles in experimental field cages in six states: California, Colorado, Nevada, Texas, Utah and Wyoming.
For the field tests, 10-foot-square cages will be placed over existing saltcedar infestations along rivers and streams. Beetle eggs or larvae will be placed in the caged areas.
U.S.D.A researchers have found no plants other than saltcedar on which the beetles feed and reproduce.
Both biological control programs will be a slow process. With success, the insects will spread out, controlling more invasive weeds in a larger area.
Not bad for a bunch of bugs!
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