The objective of this article is to extend the reported period in which flood-distributed knotweed propagules may be successfully managed using only manual labor. During a second round of early detection and rapid response (EDRR) management along the Green River in Guilford, VT, we collected and measured all Japanese knotweed propagules that had been distributed by flooding approximately 21 mo earlier, in August 2011, at a single site. Our data suggest that knotweed s.l. prioritizes the growth of new stems over new rhizomes at the start of a growing season. Because the limiting factor for successful removal of new knotweed s.l. plants by hand is the size of the rhizome system, our findings support extending the time frame for EDRR management of flood-distributed knotweed s.l. into the second spring after its initial dispersal. Additionally, in November 2013, surveys of our work sites found no new knotweed s.l. plants in locations accessible to work crews. In addition to validating our EDRR management techniques, this implies that knotweed s.l. fragment viability does not extend past the second spring following its dispersal.
Nomenclature: Knotweed sensu lato; Japanese knotweed; Polygonum cuspidatum Siebold & Zucc.; Fallopia japonica (Houtt.) Ronse Decr.; Reynoutria japonica Houtt.
Management Implications: Continuing the summer of 2012 early detection and rapid response (EDRR) work detailed in Colleran and Goodall (2014), we manually eliminated knotweed propagules distributed by Tropical Storm Irene in August 2011 in southern Vermont, during the early spring of 2013. We collected data showing that the period of opportunity can be extended for EDRR management of flood distributed knotweed s.l. propagules beyond that which we had previously established.
Additionally, our data showed that knotweed s.l. prioritized its spring growth in aboveground biomass, nearly to the exclusion of rhizome growth. The relatively large size of second-year knotweed s.l. plants compared with other vegetation in the early spring allows for highly effective visual surveys, whereas their small rhizome network, which had yet to expand from the previous year’s growth, allows for effective manual removal of the whole plant.
Although we found no new plants in November 2013 in areas accessible to manual removal, we feel this was only because of the management conducted in May 2013, as a follow-up to our summer 2012 efforts. Knotweed propagules will sprout at any point in the growing season, and significant numbers emerged at managed sites after our 2012 work was completed. The lack of plants in November 2013 suggests that our May 2013 management activities took place after the period for propagules to sprout had closed and, therefore, effectively controlled those that emerged between management efforts.
Based on our experiences, we feel we have developed a viable method to control these plants. We suggest initial removal work be performed during the first growing season to remove the fastest-emerging plants to prevent them from establishing a vigorous rhizome network. Follow-up work must be conducted either after the first growing season or early in the second growing season to ensure eradication of plants that are slower to emerge. Such a strategy is capable of eradicating new knotweed s.l. propagules following flood events. Our findings would be complimented by research that explores the effect of various forms of flooding on knotweed propagule creation and distribution.