larva on a preferred food plant, common milkweed. The milkweed may be
threatened by two invasive vines from Europe.
Pale swallow-wort in a forest in Cayuga County,
Study Targets Invasive "Dog-Strangling"
Vines By Luis
Pons June 27, 2006
Two invasive and destructive plants known as "dog-strangling" vines
are spreading uncontrolled through large areas of New York, New England and
Ontario, prompting Agricultural Research Service (ARS) and Cornell University scientists to launch a
study to find biological ways to stop them.
The targets of the three-year studywhich is being led by
Milbrath of the ARS Plant Protection Research Unit (PPRU)
in Ithaca, N.Y.are two members of the milkweed family known as pale
swallow-wort and black swallow-wort.
Both plant species originated in Europe. Pale swallow-wort
(Vincetoxicum rossicum) comes from the Ukraine, and black swallow-wort
(V. nigrum) is from southwestern Europe. On their home grounds, both are
kept in check by native natural enemies, particularly insects and diseases. But
so far, nothing on these shores has halted their advance. According to
Milbrath, the vines contain strong and unique poisons that probably limit
natural enemies here and keep deer and cattle from feeding on them.
Cornell research has shown that the pink-flowered pale swallow-wort
grows rapidly in forest understories and in open fields of undisturbed soil
throughout central and upstate New York, around the Great Lakes and in Canada.
The purple-flowered black swallow-wort prefers open areas. Its found
primarily in New York's Hudson Valley and Long Island, as well as throughout
Although both swallow-worts share the ominous "dog-strangling"
moniker, theyre actually a threat to Monarch butterflies. Pale
swallow-wort may be replacing common milkweeds in open fields upon which
monarch larvae feed. The butterflies' larvae are unable to survive on either
Also, the vines have pushed onto reduced-tillage corn and soybean
fields and impacted forest regeneration.
Working with Milbrath on the study are Cornell weed ecologist Antonio
DiTommaso; PPRU plant physiologist
Berner of the ARS
Disease-Weed Science Research Unit in Ft. Detrick, Md.; and scientists at
the ARS European Biological Control Laboratory in Montpellier, France.
ARS is the U.S. Department of
Agriculture's chief scientific research agency.