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Posted 24 August 2009. PMN Crop News.

Weed-fighting Weevils Make Themselves at Home in Montana

Source: Montana State University Press Release.

Bozeman, Montana (July 28, 2009)--Weevils that were brought into Montana 12 years ago to fight yellow toadflax have apparently established themselves in western Montana.


"The discovery -- one of the few of its kind in North America -- is good news for land owners who have hard-to-reach infestations or want to use biological controls in overall weed management," said David Weaver, a Montana State University entomologist in the Department of Land Resources and Environmental Sciences.

"They (the weevils) are ideal for situations covering large areas where other methods might be more difficult or not viable to implement," Weaver added.

Weaver was part of a team that found small, but apparently viable populations of the Mecinus stem mining weevil feeding on yellow toadflax at several Powell County sites in late May. Other team members were a local rancher, a researcher from the U.S. Forest Service, and a member of MSU Extension. Weevils were found at multiple sites, surrounding where the same weevil species was released during the mid 1990s. Researchers hadn't surveyed those sites for several years, so they were surprised to find the self-sustaining populations, Weaver said.

"Actively feeding adult weevils were found at all of the randomly selected sites evaluated in a subsequent local survey," said Sharlene Sing, a U.S. Forest Service researcher and former member of MSU's Department of Land Resources and Environmental Sciences. "It was evident that the weevils had overwintered and emerged from the previous year's yellow toadflax stems at each site."

Yellow toadflax is one of 15 plants classified as "category 1 noxious weeds" in Montana. That means it's established, generally widespread in many counties and capable of spreading rapidly and leaving land unfit or greatly limited for beneficial purposes.

Ranchers involved in the landowner-led watershed group called Blackfoot Challenge supported former MSU entomologist Robert Nowierski to start fighting the weed about 16 years ago by implementing biocontrol efforts on several ranches in the Ovando area, Weaver said. The Mecinus weevils joined the battle several years later when they were brought to Montana from Europe. The weevils and yellow toadflax are both natives of Europe.

Scientists from Colorado, Canada and Serbia conducted tests that confirmed that the newly found weevils were Mecinus janthinus, that the weevils descended from the introduced population and that the weeds were yellow toadflax, Weaver said. Confirmation was important and encouraging, he said, because the weevil species was already known to reduce Dalmatian toadflax, but typically hadn't proven to be effective on yellow toadflax in North America.

"That's rare on this particular weed, thus far," Weaver said of the weevils. "They have been established on the related weed, but this is one of the first discoveries of a self-sustaining population in the United States and North America."

Blackfoot Challenge program staff said the biocontrol effort in Powell County will now be expanded through the Blackfoot Challenge's cross-boundary efforts to coordinate and cooperate with partners, such as MSU and the U.S. Forest Service, on an ecologically and economically sustainable approach to integrated vegetation management.

Jim Stone, a local rancher and Vegetation Management Area leader for the Blackfoot Challenge, said, "The strength of our efforts to make a difference when it comes to noxious weeds and other challenges is dependent on our ability to strengthen existing partnerships, form new partnerships, learn from one another and communicate that information to our neighbors -- whether here in the Blackfoot, in Montana or across the West."

Evelyn Boswell