Dog-strangling vine Cynanchum rossicum is an exotic twinning perennial vine which has recently become invasive in southern Ontario and central New York state. It can be found in abundance within the Toronto area and is spreading quickly along road, hydro, and rail corridors. Although it is an important threat to native vegetation, especially on disturbed sites, no research has been undertaken to determine the plants’ phenology or methods to control its spread. In 1996, we undertook field studies to determine the plant’s life cycle, reproductive capacity, and methods to control its spread.
The greatest reductions in C. rossicum were observed after repeated applications of glyphosate. The results of this study indicate that two or more treatments may be required to achieve a high degree of control within one year.
Once the presence of C. rossicum has been strongly diminished, another exotic species will likely replace it, unless a desired species is first introduced. In this study, sweet white clover, an alien biennial, quickly invaded herbicided plots to replace C. rossicum as the dominant species. Thus, control itself can create another control problem, which should be anticipated in advance of designing a treatment program (although the establishment of species such as sweet white clover may be considered desirable, since nitrogen-fixing legumes are widely used as a successional cover to enhance and protect bare soil). Careful monitoring for new invasions is important, since C. rossicum seedlings can persist under the dense shade of other species, making their detection difficult.