Response of Pale Swallow-wort, <em>Vincetoxicum rossicum</em>, following Aboveground Tissue Loss: Implications for the Timing of Mechanical Control

Abstract

The growth and reproduction of Pale Swallow-wort, Vincetoxicum rossicum, were investigated following differentially timed above-ground tissue loss by clipping throughout the growing season in Ottawa, Canada. If clipping occurred early in the growing season (before June), mature plants were able to compensate in height but not in biomass or reproductive output when compared to uncut controls. This compensation in height did not seem to come at the expense of below-ground storage tissue; there was no significant difference in root mass among the control and treatment conditions. Final plant height, mass, and reproduction declined as plants were cut later in the season. Pale Swallow-wort seedlings clipped before June were able to compensate in height when compared to uncut controls. Unlike mature plants, this compensation in height did come at the expense of root mass. As the clipping treatment was performed later into the growing season, both final plant height and shoot mass decreased, while root mass increased. The best time for controlling the population spread of Pale Swallow-wort using a single cutting treatment was on or near 26 June. Plants cut earlier than this date were able resprout and produce seeds; those cut after had already produced seeds that appeared viable and may be able to germinate if the cut stems were left in the field. When a single cutting or mowing treatment is to be employed for controlling Pale Swallow-wort, we recommend cutting after the first fruits are produced but before they are fully developed.

Tolerance of Swallowworts (Vincetoxicumspp.) to Multiple Years of Artificial Defoliation and Clipping

“…Not until the fourth year did plants with smaller root masses (such as clipped four times) start to differ consistently from treatments with large root masses (comparison of means not shown, but see Figure 2). In a previous field study by McKague and Cappuccino (2005), clipping pale swallowwort once at the soil surface resulted in less stem biomass compared with nonclipped plants but had no effect on the root mass of mature plants. Previous short-term defoliation studies of swallowwort have given variable results.…”

“…Our results would additionally indicate that nonlethally damaging plants, apart from clipping (or mowing) two or four times at 8 cm, does not appreciably alter seed production. This contrasts with the study of McKague and Cappuccino (2005) in which a single clipping at ground level, properly timed, could prevent seed production. By clipping at 8 cm in our study, which is a common mowing height, the plants could more quickly regrow and flower from axillary buds.…”

“…Reported root : shoot ratios for pale swallowwort have been near or . 1, whereas for black swallowwort, they have been , 1 (McKague and Cappuccino 2005;Milbrath 2008). Nevertheless, these differences in resource allocation do not appear to have affected the resulting plant performance of individual plants under the damage regimes imposed, even after several years.…”

“…Plants that were clipped, which was a surrogate for mowing, had all stems cut 8 cm above the soil surface either once (June), twice (June, July), or four times (May, June, July, August). The clipped-once timing was based on the optimal time as determined by McKague and Cappuccino (2005) to minimize seed production from a single clipping, although they cut their plants at the soil surface.…”

“…Mechanical swallowwort control methods have been considered useful only for minimizing seed production (mowing, stem pulling, seed pod removal) or for small patches (digging out the rootstock) (Averill et al 2008;Christiansen 1998;McKague and Cappuccino 2005). In all cases, mechanical control studies were conducted for only 1 or 2 yr, with one or two clippings per season.…”