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
Management Implications: Pale swallowwort (PSW) is a highly invasive, difficult-to-control herbaceous vine that thrives in old fields but can also establish in shaded forest understories. This study sought to determine the efficacy of integrated management techniques in open-field and forest understory habitats. When PSW is cut in early July and followed in late August by application of an herbicide, the best control is obtained using different herbicides and rates in old-field compared with forest understory habitats. In the old field, two cuttings a year were ineffective and should be avoided. All herbicides reduced PSW cover, stem densities, and shoot biomass in the old field after 2 yr of combined mechanical and chemical treatments. However, cutting plus high rates of triclopyr, either as a triethylamine salt (4.87 kg ae ha−1) or butoxyethyl ester (4.87 kg ae ha−1), provided the best control. The cutting plus glyphosate treatment also provided effective control of PSW, but the cover of other species was significantly lower relative to three of four cutting plus triclopyr treatments. Regardless, it will take longer than two seasons of cutting plus herbicide applications to achieve total control of PSW in this old-field site. In the forest understory site, where PSW density was initially much lower than the old-field site, most cutting plus herbicide treatments were effective in reducing PSW cover. In general, the high rate of the triclopyr butoxyethyl ester formulation provided the best control of PSW, including a reduction in stem densities and increased cover of other species. Cutting PSW twice in each of two growing seasons was also ineffective as a management option in the forest site. Infestations of PSW in old