Japanese knotweed control with winter soil injection of chemicals targeting the rhizome system

Abstract

To achieve chemical control of aggressive creeping perennial weeds and avoid the disadvantages of conventional foliar applications, we established a winter soil‐injection method using soil‐active herbicides. Our previous study demonstrated the feasibility of the practical use of this method by showing that the regeneration from rhizomes or creeping root segments was inhibited by direct contact with chemicals in the soil. Then, a field trial was conducted on a population of Japanese knotweed. A stand of 148 plants growing on a railway bank was used for the experiment involving two herbicide treatments and an untreated control. In early March 2016, 1 L of chlorpropham (230 mg/L) or tebuthiuron (100 mg/L) was injected 15–25 cm deep into the base of each dead shoot clump. New shoot growth started in late April and became senescent in November. Aerial growth, determined as total shoot length and shoot number, significantly decreased throughout the season under both chemical treatments, without showing any injury symptoms (shoot dieback, leaf desiccation, or yellowing) that make unsightly views. In November, rhizome number was as low as 6 and 18% of the untreated control in the chlorpropham and tebuthiuron treatments, respectively. Sprouting and rooting abilities were reduced by treatment with tebuthiuron. Such marked reductions in rhizome number and viability, as well as the reduction in food reserves as estimated from diminished aerial growth, suggested probable substantial growth inhibition in the following season. Further improvement of the injection methodology would be attained from the consolidation of practical application data.

Efficacy and rates of diquat for reducing invasive knotweeds and potential for sequential use with imazapyr

“…However, an alternative explanation might lie in the potential for better, more complete coverage of the systemic herbicide applied in mid‐summer, simply as a function of reduced canopy area (Boyd et al, 2017). Our data do not allow us to distinguish these two alternatives, but does suggest that optimizing long‐term control of knotweed using sequential contact and systemic herbicide treatments warrants additional testing; ideally, these would include examination of the interactive effects on above and belowground systems (Ito & Ito, 2021; Kadlecová et al, 2022).…”

“…However, eradication of knotweed ultimately demands reduction of rhizome activity and viability (Bashtanova et al, 2009), which have been shown to vary with treatment timing (Kadlecová et al, 2022). We recommend that future studies of sequential applications should include assessment of changes in belowground and aboveground growth (Ito & Ito, 2021; Kadlecová et al, 2022); ideally these would be implemented as long‐term field‐based designs that can help inform management (Jones et al, 2018; Kadlecová et al, 2022).…”

Microwave Control of Reynoutria japonica Houtt., Including Ecotoxicological Aspects and the Resveratrol Content in Rhizomes

“…Managing invasive knotweeds is challenging due to their ability to accumulate significant below-ground reserves, allowing them to recover from various control methods, including physical, biological, chemical, and integrated approaches [ 19 , 20 , 21 , 22 ]. In the case of Japanese knotweed, some success has been achieved by focusing on seasonal resource translocation between above- and below-ground biomass and using suitable herbicide coverage or injections, such as glyphosate [ 19 , 20 , 21 , 22 ]. Another method involves physically burying rhizomes and stems [ 23 ].…”

Microwave control of Reynoutria japonica Houtt. including ecotoxicological aspect and resveratrol content in rhizomes

“…All invasive knotweeds are di cult to control, as minimum disturbance regimes permit the accumulation of signi cant below-ground reserves that allow recovery from many physical, biological, chemical, and integrated control methods. According to a few authors, in the case of Japanese knotweed, an approach that works with the seasonal resource translocation between above-and below-ground biomass and adequate herbicide coverage or injections, e.g., glyphosate, is the key to success 19,20,21,22 . The other adopted methods are the physical burying of rhizomes and stems 23 .…”