The introduced exotic vines pale and black swallow-wort rapidly have become invasive throughout regions of the northeastern United States and adjoining areas of Canada. Preliminary studies have reported that the species are allelopathic, possibly contributing to their competitive ability and invasiveness. Results from our laboratory assays indicated that swallow-wort root exudates caused significant root length reductions (e.g., 40% for butterfly milkweed and 20% for large crabgrass) and reduced germination (e.g., 25% for lettuce) of indicator species. Additional bioassays with dried swallow-wort tissues demonstrated that tissue leachates caused varied responses in indicators,with both significant stimulatory and inhibitory effects. In particular, significant congeneric interactions were noted between the two swallow-wort species. Evidence from this study of swallow-wort tissue phytotoxicity has important implications for developing effective management and habitat restoration strategies for the two invasive species.Nomenclature: Annual bluegrass, Poa annua (L.); barnyardgrass, Echinochloa crus-gallis (L.) P. Beauv.; blackswallowwort, Cynanchum nigrum (L.) Pers., non Cav.; butterfly milkweed, Asclepias tuberosa L.; common milkweed,Asclepias syriaca (L.); large crabgrass, Digitaria sanguinalis (L.) Scop.; orchardgrass, Dactylis glomerata (L.); paleswallowwort, Cynanchum rossicum (Kleopow) Borhidi; lettuce, Lactuca sativa L; tomato, Solanum lycopersicum (L.).Key words: Allelpathy; black swallowwort; interference; invasive species; pale swallowwort; phytotoxicity.
Douglass, C. H., Weston, L., & Wolfe, D. (2011). Phytotoxicity and potential allelopathy in pale (Cynanchum rossicum) and black swallowwort (C. nigrum). Invasive Plant Science and Management, 4(1), 133-141. https://doi.org/10.1614/IPSM-D-10-00021.1