Assessment of Management Strategies for Japanese knotweed (Reynoutria japonica) in Nova Scotia

Abstract

Japanese knotweed (Reynoutria japonica) is a problematic invasive species in Europe and North America that causes significant reductions in native plant diversity, increases soil erosion, leads to riverbank destruction, and can negatively affect property value and desirability. In Nova Scotia, knotweed has invaded numerous riparian zones, among other habitats, creating demand for effective and reliable management strategies. This project evaluated a variety of management strategies for their ability to reduce Japanese knotweed stem density, height, and diameter within the growing season and in the year after treatment. Chapter II evaluated the effect of cutting alone and integration of cutting and herbicide applications. Cutting significantly reduced knotweed stem height and diameter within the growing season, however stem density was not significantly reduced within the growing season or 1 YAIT. There was no significant interaction between cutting and herbicide 1 YAIT on knotweed stem density at either location. Applications of glyphosate to peak height growth and knotweed regrowth following cutting reduced knotweed stem density 1 YAIT. Applications of aminopyralid did not significantly reduce knotweed stem density 1 YAIT when applied at peak height or to regrowth. However, the re-application of treatments in the second growing season did lead to a significant reduction in knotweed stem density. Chapter III investigated if various herbicide application methods varied in their ability to control Japanese knotweed. Spot applications and stem injections of glyphosate or aminopyralid reduced knotweed stem height and diameter 1 YAIT, however knotweed stem density was only reduced by the end of the second growing season following a second application of treatments, indicating both require multiple applications to be successful strategies. A cut-stump application of glyphosate significantly reduced knotweed stem density by the end of the growing season, however knotweed completely recovered 1 YAIT. In contrast, a spot application of glyphosate resulted in stem density reductions 1 YAIT. Chapter IV evaluated if the seasonal timing of herbicide application impacted their ability to control knotweed. Peak height spot applications (mid-June) of imazapyr and glyphosate significantly reduced knotweed stem density 1 YAIT. Fall spot applications (end of September) of imazapyr, glyphosate and aminopyralid significantly reduced knotweed stem density by June of the following growing season, with aminocyclopyrachlor not providing significant stem density reductions in either timing. Japanese knotweed is a manageable species but requires considerable effort and commitment to control.