Pale Swallowwort (Vincetoxicum rossicum) Response to Cutting and Herbicides

Effective control techniques for pale swallowwort (PSW), an invasive herbaceous vine of old fields and forest understories, are limited. We conducted a 3-yr cutting and herbicide study on an adjacent old-field and forest understory site near Ithaca, NY, for control of PSW. Plants in experimental plots were cut in early July and cut again or sprayed in late August for two seasons with the isopropylamine salt of glyphosate , or one of two rates (low or high) of either triclopyr triethylamine salt (i.e., SL, SH) or triclopyr butoxyethyl ester (EL, EH). The herbicide treatments were effective in reducing PSW cover, plant (stem) density, and aboveground biomass in the old-field site, but in several cases, only after 2 yr of cutting plus herbicide application. Only the cutting plus SH treatment did not reduce PSW cover relative to the unmanaged control in the forest understory and no treatment reduced biomass. In general, the cutting plus EH treatment was most effective in reducing PSW stem densities in the forest site. The most effective herbicide treatments differed between sites. Cutting plus EH reduced PSW cover by 84% and stem density (. 5 cm) by 86% in the old-field site. Cutting plus SH effectively decreased long and short (# 5 cm) stem densities by 86 and 96%, respectively. Cutting plants twice during each of two seasons increased PSW cover by 301% and density of stems . 5 cm by 73% at this site. In the forest site, cutting plus glyphosate, or cutting plus EH or cutting plus SL and EL resulted in the greatest reductions in PSW cover (80, 76, 66, and 56%, respectively). Cover in plots cut twice per year decreased by 19%. The EH or SL treatments decreased long-stem densities by 78 and 71%, respectively. The EH treatment decreased short-stem density by 37%. These findings suggest that integrated techniques may control PSW but that effective management strategies may be habitat constrained. Nomenclature: Glyphosate; triclopyr butoxyethyl ester; triclopyr triethylamine salt; pale swallowwort, Vincetoxicum rossicum (Kleopow) Barbar., syn. European swallowwort, Cynanchum rossicum (Kleopow) Borhidi.