The “flash-kill” effect: setting the electrocution threshold for management of Japanese knotweed (Reynoutria japonica Houtt.)

Accurate quantification of the lethal threshold is critical for developing effective control strategies to mitigate severe biodiversity loss caused by extremely resilient weeds, such as the Japanese knotweed (Reynoutria japonica Houtt.). This study investigated the survival dynamics of R. japonica rhizome sprouts subjected to 60-second controlled electrocution treatments at 0 V, 20 V, 40 V, 60 V, 80 V, 100 V, 120 V, 140 V, 160 V and 180 V. Each treatment consisted of 3 sprouts (n = 3). Following exposure, the sprouts were grown under controlled conditions. The Mantel-Cox trend test revealed a highly significant, voltage-dependent decline in sprout survival throughout the 7-day monitoring period (χ²₍₁₎ = 29.028; p < 0.001), as reflected in the Kaplan-Meier survival curves. The subsequent hierarchical cluster analysis (HCA) identified three distinct physiological response zones: (i) low-impact, (ii) transitional lethal, and (iii) lethal threshold zone. The Mantel-Cox post-hoc test with the Holm-Bonferroni correction showed that sprout survival in the lethal threshold zone differed significantly from that in the low-impact and transitional lethal zones (p < 0.001), resulting in rapid mortality within 48 hours, an outcome referred to as the “flash-kill” effect. This, in turn, identified ≥ 120 V as the critical lethal threshold, leading to a complete loss of regenerative capacity and preventing further vegetative expansion. Collectively, these findings establish a quantitative baseline for precision electrocution against R. japonica and provide an empirical foundation for further evaluation of its use as a non-chemical management strategy.