CORVALLIS, Ore. – The near-eradication three decades ago of tansy ragwort, one of Oregon’s most problematic invasive species, was considered a crowning achievement because of innovative biological control methods.
But this year, tansy ragwort has flourished throughout western Oregon through a combination of weather conditions and a “down cycle” for the three insects used to control this toxic weed, continuing a disturbing recovery trend that began six years ago. Suddenly, a new generation of Oregonians, including numerous owners of small farms, ranches and other acreage, are being forced to deal with tansy before it kills their cattle or horses.
A moderate La Niña event followed by a cool, wet spring has created a double-whammy in the state, according to Andrew Hulting, an Oregon State University Extension weed management specialist.
“The same weather conditions that promote the growth of tansy also have limited the number of beneficial insects used to control the weed,” said Hulting, a faculty member in OSU’s Department of Crop and Soil Science. “The insects are in a down cycle and they may take a few years to recover.”
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