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Moth larvae released for testing in Canada could be first swallowwort antidote


Swallowwort, the bane of gardeners and environmentalists in the north country, may finally meet its match with moth larvae, which are being put to a cold-weather survival test that is considered the best hope for fighting the invasive weed.

Testing of the moth Hypena opulenta started for the first time in September in Ottawa, Ontario, as 500 larvae were released amid swallowwort patches. Scientists from the University of Rhode Island leading the study said they believe that if the moth larvae survive the winter, it could be a milestone that will enable the insect to become the only biological control agent for swallowwort.

The study, approved by the U.S. Department of Agriculture this fall, is good news for the north country, where the swallowwort has continued to spread since the 1980s, when it was discovered in the town of Henderson, said Susan J. Guise, horticulture educator at Cornell Cooperative Extension of Jefferson County. The viny weed, also known as dog-strangling vine, chokes out all other ground-level plant life and thrives in both meadows and forests. Each plant produces thousands of seeds, which remain viable for about six years. No native birds or insects feed on the weed to prevent its spread.

“The only way to slow down growth where there is a dense population is biological control; that’s why this is good news, because a biological agent is the only thing that will save us,” Mrs. Guise said. “It’s a huge problem in Northern New York, and there is a source population from the Stony Point area in Henderson that continues to spread.”

The research milestone comes after Rhode Island doctorate student Aaron Weed discovered the moth larvae feeding on swallowwort weeds in southern Ukraine. Research conducted over the following six years found that the moth larvae will only attack and survive on swallowwort weeds.

Pale and black swallowwort were accidentally introduced into the United States from Europe more than a century ago and have since spread throughout the Northeast, Midwest and Canada.

The USDA has not yet approved moth larvae to be released for testing in the U.S., Mrs. Guise said, but researchers are hopeful that could be underway in 2014. Though testing of the moth is a major step forward, she said, it usually takes about 20 years to develop a successful biological control method.

“I think we’re about halfway through the research process,” she said. “If they find out they’re cold hardy and can survive our winters, the next step would be to rear more of them for testing.”

Swallowwort, meanwhile, can be combatted only when populations are insignificant, said Mrs. Guise, who hosts workshops teaching people how to identify and combat the weed. The spraying of herbicide to kill weed patches may be successful, she said, but the plant is challenging to destroy because its seeds remain viable in the soil for long periods.

In addition to the University of Rhode Island, the moth-larvae research project involved Ukrainian plant taxonomists, Swiss, French and Canadian biocontrol specialists, and faculty and USDA researchers at Cornell University, Ithaca. It was funded by several grants from the USDA, U.S. Forest Service and Agriculture Canada.

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