Jones et al. (2018) Optimising physiochemical control of invasive Japanese knotweed

Data set underpinning the following findings: Japanese knotweed, <em>Fallopia japonica</em> var. <em>japonica</em>, causes significant disruption to natural and managed habitats, and provides a model for the control of invasive rhizome-forming species. The socioeconomic impacts of the management of, or failure to manage, Japanese knotweed are enormous, annually costing hundreds of millions of pounds sterling (GBP£) in the UK alone. Our study describes the most extensive field-based assessment of <em>F. japonica</em> control treatments undertaken, testing the largest number of physical and/or chemical control treatments (19 in total) in replicated 225 m² plots over three years. Treatments focused on phenology, resource allocation and rhizome source-sink relationships to reduce the ecological impacts of controlling <em>F. japonica</em>. While no treatment completely eradicated <em>F. japonica,</em> a multiple-stage glyphosate-based treatment approach provided greatest control. Increasing herbicide dose did not improve knotweed control, but treatments that maximised glyphosate coverage, e.g., spraying <em>vs</em> stem injection, and exploited phenological changes in rhizome source-sink relationships caused the greatest reduction of basal cover and stem density after three years. When designing management strategies, effective control of <em>F. japonica</em> may be achieved by biannual (summer and autumn) foliar glyphosate applications at 2.16 kg AE ha^-1, or by annual application of glyphosate in autumn using stem injection at 65.00 kg AE ha^-1 or foliar spray at 3.60 kg AE ha^-1. Addition of other herbicides or physical treatment methods does not improve control. This work demonstrates that considering phenology, resource allocation and rhizome source-sink relationships is critical for the control of invasive, rhizome forming species.