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Title: The Invasive Swallow-worts: What Do We Know About Their Biology and Management?

item Milbrath, Lindsey

Submitted to: International Allelopathy Congress
Publication Type: Abstract Only
Publication Acceptance Date: 8/1/2008
Publication Date: 9/21/2008
Citation: Averill, K.M., Ditommaso, A., Mohler, C.L., Milbrath, L.R. 2008. The Invasive Swallow-worts: What Do We Know About Their Biology and Management?. International Allelopathy Congress. p. 71-72.

Interpretive Summary:

Technical Abstract: The swallow-worts [Vincetoxicum rossicum (Kleopow) Barbar. and V. nigrum (L.) Moench] are nonnative, perennial, herbaceous vines in the Apocynaceae that are invading natural areas in the northeastern U.S.A. and southeastern Canada. The species form dense monospecific stands across a wide range of moisture regimes in full sun or forest understories. The dense colonies smother resident vegetation and reduce vertebrate and invertebrate biodiversity. The plants reproduce primarily by polyembryonic, wind-dispersed seeds. To date, chemical and mechanical control has been challenging. In one recent study, we investigated managing pale swallow-wort in an old-field with triclopyr and/or clipping. Two years after treatments began, swallow-wort cover was lower in plots treated with triclopyr (20%) compared with clipped-only (56%) or unmanaged (76%) plots. Regardless of clipping frequency, clipping in June or July was not effective in reducing swallow-wort stem density, cover, or follicle production. A classical biological control program was initiated by the USDA-ARS in 2004 with the goal of providing sustainable and economical long-term suppression of these two aggressive species. This long-term management approach will complement the search for effective short-term strategies, such as chemical and mechanical control. The success of this biological control effort is dependent on the availability of plant demographic data that can be modeled to determine which swallow-wort life stage(s) may be most susceptible to control efforts. Thus, we initiated several field studies in Central New York State that focused on gathering such data, including assessing (a) the degree and rate of swallow-wort vegetative expansion of the in old-field and/or forest environments and (b) seedling establishment success in habitats subjected to different disturbance regimes. In the vegetative expansion study, the number of stems per plant did not change during two growing seasons in the forested sites, but increased by 30% from July 2005 to July 2007 in the old-field sites. First-year (2007) results from the seedling establishment study varied by site and type of disturbance. At the Hanshaw site, total seedling emergence was greater on mowed plots (21%) than plots of other treatments: glyphosate + tilled (4%), glyphosate only (7 %), and control (11%). Control plots had greater emergence than glyphosate + tilled plots. At the Mt. Pleasant site, total emergence in May 2007 was 18% and did not differ between treatments. In September 2007, at Mt. Pleasant, a better drained site located at a higher elevation than the Hanshaw site, survival was 73 and 88% of May and June 2007 cohorts, respectively. At the Hanshaw site however, survival to September was 40 and 43% of May and June 2007, respectively. Additional research on these two swallow-worts is focused on determining (a) resource allocation patterns following the removal of aboveground tissue at different intensities and frequencies, (b) the duration of the juvenile phase in habitats varying in light availability, and (c) seed survival at different soil depths.