Response of pale swallowwort (Vincetoxicum rossicum) to multiple years of mowing

Authors: Biazzo, Jeromy; Milbrath, Lindsey

Submitted to: Invasive Plant Science and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/20/2019
Publication Date: 8/28/2019
Citation: Biazzo, J., Milbrath, L.R. 2019. Response of pale swallowwort (Vincetoxicum rossicum) to multiple years of mowing. Invasive Plant Science and Management. 12(3):169-175. https://doi.org/10.1017/inp.2019.22.
DOI: https://doi.org/10.1017/inp.2019.22

Interpretive Summary: Pale and black swallow-wort are European viney milkweeds that have become invasive in eastern North America. We evaluated different frequencies of mowing over six years in a high-density stand of pale swallow-wort for their impact on plant densities, cover, and reproduction. Seed production was eliminated in all years of the study with three mowings per season. Stem and root crown densities of pale swallow-wort were also reduced, especially larger-sized individuals, but only after at least 3-5 years of repeated mowing. Declines in pale swallow-wort cover were offset by increases in cover of other broad-leaf plants, although these were likely non-native species. Results for six mowings per season did not differ from three mowings. Mowing three times on a monthly basis each season is recommended to prevent seed production, but it will take several years of such mowing to reduce, but not eliminate, existing stands of pale swallow-wort.

Technical Abstract: Vincetoxicum rossicum (Kleopow) Barb., as well as its congener V. nigrum (L.) Moench, is a European viney milkweed that has become increasingly invasive in natural areas and perennial cropping systems in the northeastern United States and southeastern Canada. Previous studies of mechanical control have generally shown little efficacy although the studies were only one to two years in duration or were not conducted with naturally-occurring field populations. We assessed the effect of six seasons of mowing (0, 3, or 6 times per season on a calendar basis at 8 cm above the soil level) on stem and root crown densities, cover and follicle production of V. rossicum. Percent cover of other vegetation was also measured. Significant reductions in stem and crown densities as well as percent cover of V. rossicum generally did not occur until after 3, but more likely 5, years of mowing, and did not differ between mowing three or six times per season. In turn, the cover of other broad-leaf plants increased, although these were likely non-native species. Follicle production was eliminated in all years of the study as well. Mowing three times on a monthly basis each season should immediately prevent any seed production but will take several years to reduce, but not eliminate, existing stands of V. rossicum.