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The quest to solve the swallow-wort problem includes a trip to SwitzerlandPrintable pageTell a friendCELS NEWS RSS feed

                            By RUDI HEMPE
CELS News Editor


Aaron Weed, a URI PhD student, is spending most of this summer in Delémont, Switzerland near the French border—it’s tough duty but someone has to try to find a solution to a European invader that is a headache for farmers, a worry to foresters and a possible threat to the monarch butterflies on this side of the pond.

For his doctorate in entomology, Weed is exploring biocontrols to combat the invasive black and pale swallow-wort plants that are taking over fields and forests in the Northeast and parts of Canada.

Imported from Europe in the mid 1800s—either for ornamental or medicinal reasons—the plants resemble our native milkweed. But while we value milkweed as a plant that attracts monarch butterflies, there is no love lost for swallow-worts which invade pastures (the plant is poisonous to grazing animals) and can smother regenerative growth in forests.

“There is no good specific control,” says Weed, who notes that using a systemic herbicide such as Roundup is difficult since these weeds literally wrap around desirable plants. And because of the swallow-worts’ extensive root systems, the invader can regenerate fast, thus mechanical controls also do not work, he adds.

Hence the need for finding a biocontrol.

So Weed, who got his masters from U of Florida and his bachelors from the University of Maine, is off to Europe for the second time in search of insects that naturally control swallow-worts there. Because black and pale swallow-wort plants are not native here there are no North American natural enemies.

While there are natural controls on the plants in Europe (at least five species) researchers cannot bring them into this country without extensive testing and permitting to make sure they don’t pose a threat to our native plants.

And that, since 2006, is exactly what Weed is doing.

Recently Weed and his Major Professor, Richard Casagrande received a $90,000 CELS Cares grant to foster the three-year project. The grant will wrap up host-range test and impact studies and also pay for some student help. Other agencies, notably the USDA (Northeast IPM Program), and Agriculture Canada are helping with the funding too. In Switzerland, Weed and Casagrande collaborate with CABI, a non-profit organization that specializes in pests—agriculture, forest and weeds.

Weed says he is concentrating on three biological controls—a beetle and two moths. Brought to URI and confined in the biocontrol quarantine labs in the greenhouse complex, the insects are being evaluated.

The beetle, Eumolpus asclepiadeus is of particular interest to Weed in that in its larva stage it chews on the roots of

swallow-worts and in its adult stage attacks the tops of the plants.

The two moths being studied are Abrostola asclepiadis and Hypena opulenta. The former is widespread in Europe and latter is restricted to Eastern Europe. (The black swallow-wort is more of a Mediterranean plant and is a problem to coastal New England. The pale swallow-wort is from Eastern Europe and is more of a problem to New York State and Canada. The black swallow-wort is stubby in habit and has near-black flowers and the pale version is taller and has lighter colored flowers. Both turn into vines as they mature).

The invasives are a real pain to farmers. For example, Don Minto of the Historic Watson Farm in Jamestown raises grass-fed beef. But to control black swallow-wort in his fields he has to use chemical controls and therefore cannot be certified organic.

Some foresters, says Weed, are worried that the pale swallow-wort is affecting forest regeneration by smothering new growth.

The situation bodes ill for the majestic monarch butterflies. Monarchs like to deposit their eggs on milkweed plants but because the leaves of swallow-wort and milkweed have similar odors, monarchs sometimes deposit their eggs on swallow-worts. Research by Jennifer Dacey, a former student of Casagrande’s indicates that in RI as many as 20% of monarch eggs are laid on swallow-worts where larvae do not survive.

One of the main issues in the quarantine lab is to find out if the biocontrols will feed on native American plants. Researchers manually transfer the beetle eggs to native plants but what has to be determined is whether these insects will naturally choose native plants over the swallow-worts. Quarantine research will continue at URI this summer while Weed studies behavior in natural ecosystems in Europe.

Weed says there has been a lot of collaboration on the project which was first drafted in 2001 by Casagrande and colleagues at CABI and Cornell but which did not garner funding until recent years. His main collaborator at CABI is André Gassmann but Weed also works with USDA and Cornell and has had three Coastal Fellows working on the project plus other undergrads.

Asked to guess when a biocontrol solution will be found, Weed says that the three insects he is now considering look particularly promising, but it all depends upon the host range and impact testing currently underway. “At best, we might have a biocontrol agent ready to release in two years. On the other hand, if these agents are not adequately host-specific or effective, the search might continue for several more years.” In the meantime, he’s off to Switzerland with all its history, good food, charms and scenery. It’s a tough scientific quest but someone has to do it.


Published: June 9th, 2009.


Aaron Weed

Aaron Weed



Hypena opulenta

Hypena opulenta



Abrostola asclepiadis

Abrostola asclepiadis



Eumolpus Mating

Eumolpus mating