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

• Published in: Weed biology and management 2021-12, Vol.21 (4), p.202-208
• Main Authors: Ito, Misako, Ito, Kanji
• Format: Article
• Language: English
• Subjects: Aquatic plants; Chemical control; Chemical treatment; Chemicals; chlorpropham; creeping perennial weed; Desiccation; Dieback; Feasibility studies; Foliar applications; Herbicides; Injection; invasive species; Polygonaceae; Regeneration; Rhizomes; Rooting; Soil chemistry; Soils; soil‐active herbicide; tebuthiuron; Winter; Yellowing
• ISSN: 1444-6162; 1445-6664
• DOI: 10.1111/wbm.12239

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.