Print PageInvasive knotweeds, including Japanese knotweed, (Fallopia japonica), Giant knotweed (F. sachalinensis) and their hybrid cross Fallopia x bohemica pose a serious threat to North American habitats. The plants are invasive in 41 states and 8 Canadian provinces. They form dense monocultures that threaten biodiversity, cause significant damage to transportation and urban infrastructure, exacerbate flooding and affect water quality for aquatic organisms. To date there has been limited success with chemical or mechanical control tactics for knotweeds and neither approach is economically or ecologically feasible over the areas requiring treatment. Aphalara itadori is a promising biological control agent for knotweeds in North America. In this presentation, we consider the implications of the east-west international border for the implementation of biological control of an invasive plant that follows north-south ecological gradients in the Pacific Northwest.
Results/Conclusions
Examination of existing point data for knotweed distribution in the PNW indicates sampling gaps and potential areas of spread within jurisdictions and across borders. Climatic conditions including annual degree days, mean-annual minimum temperatures and precipitation at knotweed sites in British Columbia, Washington and Oregon were modeled in BioSIM, using weather normals and long-term daily-weather data. These conditions were compared to published biotic thresholds for knotweed (degree day = 2505 DD, min. temperature = -30.2oC, precipitation = 735mm) to estimate its potential range. The key limiting climatic thresholds varied between and within the three jurisdictions; in BC degree-days were most limiting for Japanese knotweed whereas in Washington and Oregon precipitation was the most important single factor. There are still significant areas for new invasion in all jurisdictions associated with climate thresholds. Habitat suitability maps generated using local parameters will enable better targeting of knotweed surveys based on the risk of knotweed establishment. Consideration of shifts in temperature associated with climate change models suggest an even larger potential for spread that varies by jurisdiction.
Knotweed genotypes are extremely variable throughout the invaded ranges of North America, the UK and Europe. Variable climatic thresholds across the invaded region of the PNW may result in selection for differing knotweed genotypes locally. In pre-release screening experiments, the performance of A. itadori differed significantly among knotweed clones collected from BC. This may affect the overall impact of the biocontrol agent, depending on the host-suitability of the dominant knotweed genotypes within a region or country. The success of biocontrol may also be affected by differing regulatory environments in Canada and the US.
