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Abstract

Control and management of invasive plants frequently differs from agricultural weed control as plant establishment and development progresses in less intensively managed systems. This is particularly the case for rhizome-forming invasive plants, such as Japanese knotweed ( Fallopia japonica var. japonica ) as minimum disturbance regimes permit the accumulation of significant below ground reserves that allow recovery from many physical, biological, chemical and integrated control methods. Here, we review the ongoing work of Jones, who established the world's largest and longest running invasive knotweed field trial. Using an integrated weed management (IWM) approach to testing, this research evaluated 19 different control treatments over three years to minimise pesticide use and increase the sustainability of controlling this ecologically and economically damaging species. Through consideration of plant biology, it was found that glyphosate-based herbicide treatments that exploited phenological changes in rhizome source-sink were significantly more effective than all other treatments. These results provide a roadmap to the more effective and efficient control of rhizome-forming invasive plants and emphasise the importance of scale appropriate empirical evidence to inform regulators when considering non-agricultural weed control. Within intensively managed arable agricultural systems, weed control is directed toward immature annual and perennial plants, during a 'critical period' extending for a relatively short time after crop emergence. This is because at this time, resource depletion by weed species may exert a major negative effect upon crop yield. Agronomic weed management may be achieved using a range of weed control methods, including: cultural/preventative (e.g. soil cultivation, disrupting weed establishment), physical (mechanical methods or hand weeding), biological (biocontrol or bioherbicides), chemical (plant protection products; PPPs) and integrated weed management (IWM). True IWM systems combine cultural, physical, biological and/or chemical methods; integrated herbicide management systems use a range of PPPs to mitigate selection of resistant weed populations. In contrast, control of invasive weed species, or invasive alien plants (IAPs) is commonly undertaken in less intensively managed systems, or unmanaged areas such as abandoned agricultural land, riparian areas and brownfield sites. Here, IAPs tend to be large and well-established so that plant persistence and development processes are often unhindered by weed control methods typically applied in agriculture. This is particularly true of rhizome-forming invasive species, such as Japanese knotweed ( Fallopia japonica var. japonica ) where minimal disturbance regimes permit the long-term development of significant carbohydrate reserves within perennating rhizome organs below the soil surface (>50 cm). Storage reserves permit recovery from repeated intentional disturbance and biological control; while physical size, depth, resilience and strong seasonal changes in source-sink strength of such organs preclude effective chemical control using many herbicides, as insufficient herbicide active ingredient is accumulated within storage tissues. There are strong environmental, ecological and economic cases for the management of IAPs to minimise their negative impacts. However, invasive plant management is hindered by the absence of scale appropriate empirical evidence to support control method selection and plant traits which are effective against control, e.g. rhizome bud bank. Consequently, control programmes may have less than optimal results in terms of economic and environmental sustainability. Terminology is critically important when defining clear programme objectives (i.e. control, management, eradication) and long-term assessment of IAP control and post-treatment habitat recovery is needed to establish best practice. 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 is the key to success. Physical disruption of the plant or increasing use of herbicide application will not give better control and may be less effective and costly. There is increasing public concern (real and perceived) about the widespread use of herbicides, and glyphosate in particular, resulting in increased PPP deregulation and reduced concentration and application rates. Experimental data that define best practice are essential to inform regulators when considering non-agricultural weed control. While the use of PPPs to control perennial IAPs is relatively small, the detrimental environmental, economic and amenity impacts are significant, such that the loss of effective PPPs should be of concern. In the absence of glyphosate, the only effective alternative for Japanese knotweed control would be complete physical excavation and disposal which would be significantly more expensive and arguably more environmentally harmful due to increased associated CO 2 emissions and the risk of further spread.

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... Unfortunately, economic evaluation of the methods is only rarely available (Hocking et al. 2023). The results from long-term sustainable control are missing, as the studies cover only a limited time span or are based on small study sites, or even use only experimental data from laboratory or experimental gardens (Kettenring and Adams 2011;Jones and Eastwood 2019). Nevertheless, the practical nature protection and land managers need the long-term studies that can be applied on a large scale (Pergl et al. 2020b). ...
... The proper application of herbicide is also crucial. Glyphosate dosage/application rates are discussed by Delbart et al. (2012), Jones and Eastwood (2019), or Kadlecová et al. (2022). Also, several literature sources recommend to reduce above-ground biomass prior to herbicide application (Jones and Eastwood 2019;Hocking et al. 2023). ...
... Glyphosate dosage/application rates are discussed by Delbart et al. (2012), Jones and Eastwood (2019), or Kadlecová et al. (2022). Also, several literature sources recommend to reduce above-ground biomass prior to herbicide application (Jones and Eastwood 2019;Hocking et al. 2023). ...
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One of the most problematic invasive species in Europe are knotweeds from genus Reynoutria (Fallopia) which have significant negative impact on the native communities as well on human activities. Therefore, they are a target of many control programmes. Due to their high regeneration potential, their management is problematic, and only chemical treatment is reported to be sufficiently effective. The aim of this paper was to describe and analyse the patterns of Reynoutria invasion under long-term chemical treatment with glyphosate-based herbicide in The Morávka river floodplain, Czech Republic. The data covers 17 years of management which started with the European project “Preservation of alluvial forest habitats in the Morávka river basin”. We focus on (i) assessment of Reynoutria distribution during long-term management, (ii) analysis of the change of distribution according to the habitat, and (iii) discussion of the optimal management strategy based on the long-term data. Distribution data was obtained using GNSS field mapping. Before the start of the study in 2007, Reynoutria stands covered 29% of the study area (96.9 ha). As a result of systematic whole area chemical management, the extent decreased to 19.6% (65.3 ha) in 2009, and even reached 14.5% (48.2 ha) in 2013, three years after its end. Due to implementation of local chemical management in the following years, the area of Reynoutria was maintained at similar level, with minimum value 41.8 ha in 2018 and a slight increase in recent mapping in 2023. Beside the extent, the structure and coverage of invaded sites was analysed. There was a clear trend of fragmentation of larger polycormons with high coverage into many smaller and less dense ones as a result of chemical spraying. The average size of Reynoutria stand decreased from 0.61 ha in 2007 to half in 2013 (0.32 ha) to 0.15 ha in 2023. Testing of the effects of time, habitat, and biotope did not reveal significant differences of changes of extent and abundance over different environments (forest, open, bare ground), which indicates that there are no differences in reaction to management in the studied habitat and vegetation types. Our study provides a robust and unique overview of the invasion, reinvasion, and suppression dynamics for an important invasive species. If herbicide management is used, chemical treatment must be quite long-term as even three years of intensive glyphosate foliar spray application was not sufficient for the complete eradication of Reynoutria. Therefore, we propose the following procedure for effective chemical management of Reynoutria: 1) In largely infested sites, the first step is to reduce the distribution of Reynoutria stands to isolated polycormons. This phase can last 3–5 years. 2) After reaching the state of sparse distribution of Reynoutria, we recommend herbicide application only in periods of every 3–5 years depending on the local context and rate of regrowth. 3) At sites exposed to soil disturbances, where the soil is contaminated by fragments of Reynoutria rhizomes, there is a need to apply herbicide immediately to target newly resprouting individuals.
... 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 . ...
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Japanese knotweed ( Reynoutria japonica Houtt.) is Poland's invasive weed, of no efficient control method. The rhizomes of this species are rich in resveratrol. In this work, we evaluated 1) the effectiveness of electromagnetic microwaves (MV) in destroying Japanese knotweed using an original device HOGWEED (MV of 2450 MHz); 2) the ecotoxic effect of the MV on the soil environment; 3) the resveratrol content in knotweed rhizomes after MV treatment. The field studies were carried out in 2022 in southern Poland. Cut plants were MV treated at times: 5.0–25.0 min. The MV efficiency was checked 10 and 56 days after treatment (DAT). After MV treatment, fresh soil samples were taken to analyze their ecotoxicity. As a result, at 56 DAT, knotweed was controlled if MV was used for at least 20.0 min. The MV did not affect the soil ecotoxicity. The MV-treated soils were classified as non-toxic or low-toxic. To analyze the resveratrol content, healthy knotweed rhizomes were dug out and treated with MV in laboratory at times: 2.5–10.0 min, and analyzed for the resveratrol content in HPLC-MS/MS. In result, the resveratrol in the rhizomes significantly decreased following MV exposure in a time-depending manner.
... and human health. This increases the risk of deregulation, jeopardising effective knotweed management 26 and wider IAP control; particularly given that rates of biological invasion have not yet reached saturation 27 . ...
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Sustainable land management encompasses a range of activity that balance land use requirements with wider conservation and ecosystem impact considerations. Perennial invasive alien plants (IAPs), such as Japanese knotweed, cause severe ecological and socio-economic impacts, and methods to control their spread also come at a cost. Synthetic herbicides are generally viewed as less sustainable and more ecologically damaging than alternative approaches. Here we used a comparative Life Cycle Assessment to evaluate the sustainability of herbicide-based management approaches and physical alternatives, using a large-scale Japanese knotweed field study as a model IAP system. Glyphosate-based methods elicited the lowest environmental impacts and economic costs during production. Geomembrane covering and integrated physiochemical methods were the costliest and imposed the greatest impacts. We discuss the costs and benefits of chemical and physical approaches for the sustainable management of invaded land and question how sustainable environmental stewardship is defined for the control of IAPs.
... Herbicide treatment is well described as a means of reducing growth of R. japonica over several years when applied correctly (Jones et al., 2018;Jones & Eastwood, 2019). The findings of this study, that there was no significant difference between crowns sampled from treated and untreated sites for regenerated stem diameter, maximum stem height and maximum growth increments, were therefore surprising because they indicate that the crowns were all equally able to produce new growth, regardless of treatment history. ...
Article
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Reynoutria japonica (Japanese knotweed) is a problematic invasive plant found in many areas of Europe and North America. Notably, in the UK, the species can cause issues with mortgage acquisition. Control of R. japonica is complicated by its ability to regenerate from small fragments of plant material; however, there remains uncertainty about how much (in terms of mass) rhizome is required for successful regeneration. This study investigated the ability of crowns and rhizomes with different numbers of nodes to regenerate successfully from three sites in the north of England, UK. Two of the sites had been subject to herbicide treatment for two years prior to sampling and the third site had no history of herbicide treatment. No significant differences were observed in regenerated stem diameter, maximum height of stem and maximum growth increments among crowns. All traits measured from the planted crowns were significantly greater than those of the planted rhizome fragments and at least one node was necessary for successful regeneration of rhizomes. The smallest initial fragment weight to regenerate and survive the experiment was 0.5 g. Subjecting all plant material to desiccation for 38 days resulted in no regrowth (emergence or regeneration) after replanting. These findings suggest that desiccation could be a valuable management strategy for small to medium scale infestations common in urban settings.
... This undermines the sustainability of long-term control programmes for these species, resulting in further spread and dispersal in the environment with no discernible management benefit (i.e. 'the cure is worse than the disease'; Kettenring and Adams 2011;Jones et al. 2018;Jones and Eastwood 2019). ...
Article
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Japanese knotweed (Reynoutria japonica Houtt.) is Poland's invasive weed, for which there is no efficient control method. The rhizomes of this species are rich in resveratrol. In this work, we evaluated (1) the effectiveness of electromagnetic microwaves (MV) in destroying Japanese knotweed using an original device, HOGWEED (MV of 2450 MHz), (2) the ecotoxic effect of the MV on the soil environment, and (3) the resveratrol content in knotweed rhizomes after MV treatment. The field studies were carried out in 2022 in southern Poland. Cut plants were MV-treated for times of 5.0-25.0 min. The MV efficiency was checked 10 and 56 days after treatment (DAT). After MV treatment, fresh soil samples were taken to analyze their ecotoxicity. As a result, at 56 DAT, knotweed was controlled if MV was used for at least 20.0 min. The MV did not affect the soil ecotoxicity. The MV-treated soils were classified as non-toxic or low-toxic. To analyze the resveratrol content, healthy knotweed rhizomes were dug out, treated with MV in the laboratory at 2.5-10.0 min, and analyzed for resveratrol content in HPLC-MS/MS. As a result, the resveratrol in the rhizomes significantly decreased in a time-dependent manner following MV exposure.
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1. Invasive plants can reduce biodiversity, alter ecosystem functions and have considerable economic impacts. Invasive plant control is therefore the focus of restoration research in invader-dominated ecosystems. Increasing the success of restoration practice requires analysis and synthesis of research findings and assessment of how experiments can be improved. 2. In a systematic review and meta-analysis of invasive plant control research papers, we asked: (i) what control efforts have been most successful; and (ii) what invasive plant control research best translates into successful restoration application? 3. The literature evaluated typically described experiments that were limited in scope. Most plot sizes were small (<1 m2), time frames were brief (51% evaluated control for one growing season or less) and few species and ecosystems (predominantly grasslands) were studied throughout much of the literature. The scale at which most experiments were conducted potentially limits relevance to the large scales at which restorations typically occur. 4. Most studies focused on invasive species removal and lacked an evaluation of native revegetation following removal. Few studies (33%) included active revegetation even though native species propagule limitation was common. Restoration success was frequently complicated by re-invasion or establishment of a novel invader. 5. Few studies (29%) evaluated the costs of invasive species control. Additionally, control sometimes had undesirable effects, including negative impacts to native species. 6. Synthesis and applications. Despite a sizeable literature on invasive plant control experiments, many large-scale invasive plant management efforts have had only moderate restoration success. We identified several limitations to successful invasive species control including: minimal focus on revegetation with natives after invasive removal, limited spatial and temporal scope of invasive plant control research, and incomplete evaluation of costs and benefits associated with invasive species management actions. We suggest that information needed to inform invasive plant management can be better provided if researchers specifically address these limitations. Many limitations can be addressed by involving managers in research, particularly through adaptive management.
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The invasion of NW Europe by a single clone of male-sterile Fallopia japonica var. japonica by purely vegetative reproduction has demonstrated that reproduction by seed and the genetic diversity associated with it may not be an essential feature of plant invasions, at least in the short term. What is less well known is that a significant proportion of the Japanese Knotweed s.l. involved is not F. japonica var. japonica, but the hybrid between it and F. sachalinensis–F.×bohemica. This hybrid is able to backcross to either parent with the potential to replace the missing male F. japonica; by the same process, the hybrid is generating the genetic diversity so conspicuously lacking in F. japonica. In terms of understanding the population structure in a particular country, it is important to be able to identify hybrids and putative back-crosses. We bring together a mixture of published and unpublished information to provide a comprehensive section on morphological and anatomical aids to identification. Regeneration of plants from stem and rhizome fragments varies by taxon, as do responses to control techniques, underlining the importance of correct identification of these plants. In this paper we look closely at this group of taxa, with special emphasis on the role played by hybridization, with an examination of the genetic make up of seedlings produced in the wild or by artificial hybridizations, and the implications that this will have on the future directions of the invasion process.
Article
Pathways describe the processes that result in the introduction of alien species from one location to another. A framework is proposed to facilitate the comparative analysis of invasion pathways by a wide range of taxa in both terrestrial and aquatic ecosystems. Comparisons with a range of data helped identify existing gaps in current knowledge of pathways and highlight the limitations of existing legislation to manage introductions of alien species. The scheme aims for universality but uses the European Union as a case study for the regulatory perspectives. Alien species may arrive and enter a new region through three broad mechanisms: importation of a commodity, arrival of a transport vector, and/or natural spread from a neighbouring region where the species is itself alien. These three mechanisms result in six principal pathways: release, escape, contaminant, stowaway, corridor and unaided. Alien species transported as commodities may be introduced as a deliberate release or as an escape from captivity. Many species are not intentionally transported but arrive as a contaminant of a commodity, for example pathogens and pests. Stowaways are directly associated with human transport but arrive independently of a specific commodity, for example organisms transported in ballast water, cargo and airfreight. The corridor pathway highlights the role transport infrastructures play in the introduction of alien species. The unaided pathway describes situations where natural spread results in alien species arriving into a new region from a donor region where it is also alien. Vertebrate pathways tend to be characterized as deliberate releases, invertebrates as contaminants and plants as escapes. Pathogenic micro‐organisms and fungi are generally introduced as contaminants of their hosts. The corridor and unaided pathways are often ignored in pathway assessments but warrant further detailed consideration. Synthesis and applications. Intentional releases and escapes should be straightforward to monitor and regulate but, in practice, developing legislation has proved difficult. New introductions continue to occur through contaminant, stowaway, corridor and unaided pathways. These pathways represent special challenges for management and legislation. The present framework should enable these trends to be monitored more clearly and hopefully lead to the development of appropriate regulations or codes of practice to stem the number of future introductions.
Article
Rhododendron ponticum is an invasive species in many countries, including the United Kingdom, Ireland, Belgium, and France. It poses a serious threat to native flora and fauna, as it is capable of altering entire seminatural communities through its vigorous spread. Control is essential if the conservation value of some communities, such as oak woodland and lowland heath, are to be successfully maintained. Commonly used interventions are herbicide application, herbicide application postcut, and cutting (manual or mechanical) alone. Various techniques have been developed to apply these interventions, but often retreatment of the area is required, increasing the cost of control. Here, we evaluate the effectiveness of some commonly used interventions for R. ponticum control using a systematic review methodology. Eleven studies provided data for statistical analysis. Meta-analyses of captured data show that postcut application of the herbicide Glyphosate or applying the herbicides Metsulfuron-methyl or Imazapyr (no cut) can effectively reduce a R. ponticum stand. There is insufficient available experimental evidence for effectiveness of any other intervention. The systematic review process has demonstrated the lack of replicated studies with controls or long-term monitoring and increases the call for more rigorous monitoring of all conservation management interventions. The quality of experimental evidence of the effectiveness of some interventions contrasts with the acceptance of their use through dissemination of experience. The collection and objective review of experience will require active collaboration of organizations concerned with R. ponticum control.
Japanese Knotweed s.l. Taxa and Introduced Petasites Species: Biosystematics, Ecology and Control
  • D Jones
Jones D (2015). Japanese Knotweed s.l. Taxa and Introduced Petasites Species: Biosystematics, Ecology and Control. PhD Thesis, Swansea University, Swansea, UK.
Are Japanese knotweed (Fallopia japonica) control and eradication interventions effective? Centre for Evidence-Based Conservation (CEBC) Systematic Review No
  • T J Kabat
  • G B Stewart
  • A S Pullin
Kabat TJ, Stewart GB, Pullin AS (2006). Are Japanese knotweed (Fallopia japonica) control and eradication interventions effective? Centre for Evidence-Based Conservation (CEBC) Systematic Review No. 21.
Development of strategies for the control and eradication of Japanese knotweed
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Macfarlane J (2011). Development of strategies for the control and eradication of Japanese knotweed. PhD Thesis, University of Exeter, Exeter, UK.
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Thompson K (2000). Where Do Camels Belong? The story and science of invasive species. Profile Books Ltd, London, UK.
The Economic Cost of Invasive Non-Native Species on Great Britain
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  • A Harris
Williams F, Eschen R, Harris A, et al. (2010). The Economic Cost of Invasive Non-Native Species on Great Britain. CABI, Wallingford, UK.