A new ARS test could reveal whether two Russian species of rust--a disease-causing, plant fungus--can be added to the natural arsenal against leafy spurge. This noxious weed invaded the United States from Eurasia early in the 19th century. Chemical controls are expensive and impractical, but rusts and other natural pathogens can reduce spurge's vigor and even kill it. ARS scientists are evaluating two rust species found outside the Russian city of Stavropol. At a site near Stavropol, they transplanted spurge plants from Montana next to Russian spurge plants infected with the rusts. If the Montana weed readily becomes infected and succumbs, this will be a sign that American spurge has lost some rust resistance possessed by its Russian ancestors. In turn, that will increase the two rusts' potential to help U.S. ranchers battle the weed.
Range Weeds and Cereals Laboratory, Bozeman, MT
Tony Caesar, (406) 994-6003

A bronze Chinese beetle may also join the corps of beneficial insects already imported to fight leafy spurge. Several years ago in China, an ARS scientist now based in Florida discovered the spurge-fighting potential of the 1/8-inch-long beetle, Aphthona chinchihi. Now, ARS researchers in Montana and France are conducting tests to ensure that this promising beetle won't significantly impact plants that are spurge relatives. Next, the scientists expect to seek federal approval to free the beetle in America. Spurge grows one to three feet high, crowds out forage and costs ranchers and others $100 million a year in losses, including reduced forage and beef production.
Aquatic Weed Control Research, Fort Lauderdale, FL
Robert W. Pemberton, (305) 475-0541

Musk thistle appears to have met its match in Texas in the flower weevil, a tiny European insect imported as a biological control. Musk thistles have spread in Texas from a single county in 1975 to at least 28 counties in 1993, infesting pastures, roadsides and recreation areas. To combat this wandering weed, ARS scientists released flower weevils (Rhincyllus conicus) at Kerrville in 1987. By 1993, 90 percent of thistles at the release site were infested with the weevils. Seed production was reduced an average of 81 percent. Also, the weevil had spread more than three miles from the release site. Flower weevils had not been previously released in a state as far south as Texas, although they have successfully controlled thistles in Missouri, Montana and Virginia. Plans are being made to distribute the weevil to other areas in Texas and Louisiana that are infested with musk thistle.
Grassland, Soil and Water Research, Temple, TX
Paul E. Boldt, (817) 770-6530

A beneficial mite from Europe could fight thorny gorse thickets that invade many Pacific Coast pastures and recreation areas. ARS scientists raised gorse spider mites, known as Tetranychus lintearius, for Oregon and California--the first states to use the mites. No bigger than a pinpoint, the rust-colored, eight-legged mites suck gorse's cell contents. Gorse has yellow flowers, but their beauty is costly to ranchers along the Pacific Coast and in Hawaii. The weed forms nearly impenetrable thickets that block livestock from reaching nutritious forage plants. Gorse and the mites are both native to western Europe. ARS scientists ran tests that show the mites won't feed on lupine, a gorse relative. The mites also don't nip other plants, animals or people. That's unlike gorse, which pricks hikers and campers with its thorns.
Plant Protection Research, Albany, CA
Charles E. Turner/B. David Perkins, (510) 559-5975

Last Updated: December 12, 1996
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