Integrating restoration and ecologically based weed management practices for invasive knotweed control

Japanese knotweed is an invasive perennial shrub that dominates riparian ecosystems. Effective management techniques are currently limited to repeated annual herbicide applications and there is little science-based information about which control tactics result in the greatest management success. Restoration of invaded sites to a functioning riparian plant community is needed to prevent re-infestation of Japanese knotweed or other invasive weed species. Field and greenhouse experiments were initiated in fall of 2007 to generate this information on Japanese knotweed management. A greenhouse experiment was conducted to evaluate the efficacy of the experimental herbicide aminocyclopyrachlor methyl ester for Japanese knotweed control. Treated plants were unable to produce new shoots from underground rhizomes indicating that aminocyclopyrachlor is an effective control. This level of Japanese knotweed suppression is comparable to imazapyr and surpasses the level of control that glyphosate provided under greenhouse conditions. A field experiment was initiated in the Nehalem River watershed in western Oregon to evaluate the integration of chemical weed management with restoration of the site to a diverse native grass plant community. We documented that native grasses could be established at this site, but the long-term survival of these grasses was poor. This result indicates that methods for simultaneous chemical control of invasive knotweed and restoration of sites need to be investigated further. The most effective chemical treatment in terms of visual injury and reduced Japanese knotweed biomass and cost of application was glyphosate applied at a rate of 4.21 kg ae/ha for a cost of $160/ha. A secondary experiment evaluating herbicide tank mixtures of glyphosate with imazapyr, imazapyr with aminopyralid, and triclopyr with 2,4-D was conducted at the same site. The most effective chemical treatment in terms of Japanese knotweed control and cost of application for the tank mixture experiment was imazapyr with aminopyralid applied at rates of 1.12 kg ae/ha (imazapyr) and 0.12 kg ae/ha (aminopyralid) for a cost of$346/ha

Elucidating the Population Dynamics of Japanese Knotweed Using Integral Projection Models

Plant demographic studies coupled with population modeling are crucial components of invasive plant management because they inform managers when in a plant’s life cycle it is most susceptible to control efforts. Providing land managers with appropriate data can be especially challenging when there is limited data on potentially important transitions that occur belowground. For 2 years, we monitored 4 clonal Japanese knotweed (Polygonum cuspidatum) infestations for emergence, survival, shoot height until leaf senescence, dry shoot biomass after senescence, and rhizome connections for 424 shoots. We developed an integral projection model using both final autumn shoot height and shoot biomass as predictors of survival between years, growth from year to year, and number of rhizomes produced by a shoot (fecundity). Numbers of new shoots within an infestation (population growth rate λ) were projected to increase 13-233% in a year, with the greatest increase at the most frequently disturbed site. Elasticity analysis revealed population growth at 3 of the 4 sites was primarily due to ramet survival between years and to yearto- year growth in shoot height and shoot biomass. Population growth at the fourth site, the most disturbed, was due to the large production of new rhizomes and associated shoots. In contrast to previous studies, our excavation revealed that most of the shoots were not interconnected, suggesting rhizome production may be limited by the size or age of the plants, resource availability, disturbance frequency, or other factors. Future integration of plant population models with more data on belowground growth structures will clarify the critical stages in Japanese knotweed life cycle and support land managers in their management decisions

A simulation model of Rhizome networks for Fallopia japonica (Japanese Knotweed) in the United Kingdom

Fallopia japonica (Japanese knotweed) is an aggressively invasive herbaceous perennial that causes substantial economic and environmental damage in the United Kingdom (UK). As such, it is of considerable concern to councils, environmental groups, private landowners and property developers. We construct a 3D correlated random walk model of the development of the subterranean rhizome network for a single stand of F. japonica. The formulation of this model uses detailed knowledge of the morphology and physiology of the plant, both of which differ in the UK to that of its native habitat due to factors including a lack of predation and competition, longer growth seasons and favourable environmental conditions in the UK. Field data obtained as a part of this study are discussed and used in the model for parameterisation and validation. The simulation captures the field data well and predicts, for example, quadratic growth in time for the stand area. Furthermore, the role of a selection of parameters on long-term stand development are discussed, highlighting some key factors affecting vegetative spread rates

Regional differences in clonal Japanese knotweed revealed by chemometrics-linked attenuated total reflection Fourier-transform infrared spectroscopy

Abstract: Background: Japanese knotweed (R. japonica var japonica) is one of the world’s 100 worst invasive species, causing crop losses, damage to infrastructure, and erosion of ecosystem services. In the UK, this species is an all-female clone, which spreads by vegetative reproduction. Despite this genetic continuity, Japanese knotweed can colonise a wide variety of environmental habitats. However, little is known about the phenotypic plasticity responsible for the ability of Japanese knotweed to invade and thrive in such diverse habitats. We have used attenuated total reflection Fourier-transform infrared (ATR-FTIR) spectroscopy, in which the spectral fingerprint generated allows subtle differences in composition to be clearly visualized, to examine regional differences in clonal Japanese knotweed. Results: We have shown distinct differences in the spectral fingerprint region (1800–900 cm− 1) of Japanese knotweed from three different regions in the UK that were sufficient to successfully identify plants from different geographical regions with high accuracy using support vector machine (SVM) chemometrics. Conclusions: These differences were not correlated with environmental variations between regions, raising the possibility that epigenetic modifications may contribute to the phenotypic plasticity responsible for the ability of R. japonica to invade and thrive in such diverse habitats

Potential phytotoxic and shading effects of invasive Fallopia (Polygonaceae) taxa on the germination of dominant native species

Two species of the genus Fallopia (F. sachalinensis, F. japonica, Polygonaceae) native to Asia, and their hybrid (F. ×bohemica), belong to the most noxious plant invaders in Europe. They impact highly on invaded plant communities, resulting in extremely poor native species richness. The low number of native species in invaded communities points to the possible existence of mechanisms suppressing their germination. In this study we assessed, under laboratory conditions, whether there are phytotoxic effects of the three Fallopia congeners on seed germination of three target species: two native species commonly growing in habitats that are often invaded by Fallopia taxa (Urtica dioica, Calamagrostis epigejos), and Lepidium sativum, a species commonly used in allelopathic bioassays as a control. Since Fallopia taxa form dense stands with high cover, we included varying light conditions as an additional factor, to simulate the effects of shading by leaf canopy on germination. The effects of aqueous extracts (2.5%, 5.0%, and 0% as a control) from dry leaves and rhizomes of the Fallopia congeners on germination of the target species were thus studied under two light regimes, simulating full daylight (white light) and light filtered through canopy (green light), and in dark as a control regime. Rhizome extracts did not affect germination. Light treatments yielded inconclusive results, indicating that poor germination and establishment of species in invaded stands is unlikely to be caused by shading alone. However, we found a pronounced phytotoxic effect of leaf extracts of Fallopia taxa, more so at 5.0% than 2.5% extract concentration. Fallopia sachalinensis exerted the largest negative effect on the germination of Urtica dioica, F. ×bohemica on that of C. epigejos, and F. japonica had invariably the lowest inhibitory effect on all test species. The weak phytotoxic effect of F. japonica corresponds to the results of previous studies that found this species to be generally a weaker competitor than its two congeners. Although these results do not necessarily provide direct evidence for allelopathic effects in the field, we demonstrate the potential phytotoxic effect of invasive Fallopia taxa on the germination of native species. This suggests that allelopathy may play a role in the impact of Fallopia invasion on species diversity of invaded communities

Potential phytotoxic and shading effects of invasive Fallopia (Polygonaceae) taxa on the germination of dominant native species

Two species of the genus Fallopia (F. sachalinensis, F. japonica, Polygonaceae) native to Asia, and their hybrid (F. ×bohemica), belong to the most noxious plant invaders in Europe. They impact highly on invaded plant communities, resulting in extremely poor native species richness. The low number of native species in invaded communities points to the possible existence of mechanisms suppressing their germination. In this study we assessed, under laboratory conditions, whether there are phytotoxic effects of the three Fallopia congeners on seed germination of three target species: two native species commonly growing in habitats that are often invaded by Fallopia taxa (Urtica dioica, Calamagrostis epigejos), and Lepidium sativum, a species commonly used in allelopathic bioassays as a control. Since Fallopia taxa form dense stands with high cover, we included varying light conditions as an additional factor, to simulate the effects of shading by leaf canopy on germination. The effects of aqueous extracts (2.5%, 5.0%, and 0% as a control) from dry leaves and rhizomes of the Fallopia congeners on germination of the target species were thus studied under two light regimes, simulating full daylight (white light) and light filtered through canopy (green light), and in dark as a control regime. Rhizome extracts did not affect germination. Light treatments yielded inconclusive results, indicating that poor germination and establishment of species in invaded stands is unlikely to be caused by shading alone. However, we found a pronounced phytotoxic effect of leaf extracts of Fallopia taxa, more so at 5.0% than 2.5% extract concentration. Fallopia sachalinensis exerted the largest negative effect on the germination of Urtica dioica, F. ×bohemica on that of C. epigejos, and F. japonica had invariably the lowest inhibitory effect on all test species. The weak phytotoxic effect of F. japonica corresponds to the results of previous studies that found this species to be generally a weaker competitor than its two congeners. Although these results do not necessarily provide direct evidence for allelopathic effects in the field, we demonstrate the potential phytotoxic effect of invasive Fallopia taxa on the germination of native species. This suggests that allelopathy may play a role in the impact of Fallopia invasion on species diversity of invaded communities

The relationship between substrate characteristics and Japanese knotweed invasion along the Saco River, Maine and New Hampshire

Japanese knotweed (Fallopia japonica) is an aggressive invasive plant that spreads via several mechanisms making it hard to control. Currently, little is known about Japanese knotweed invasion in riparian habitats. A total of 46 soil samples from both invaded and uninvaded sites (32 total locations) along the Saco River in Maine and New Hampshire were examined to see whether physical and chemical characteristics were similar among knotweed-invaded sites and what may lead to successful establishment by knotweed. The majority of sites were dominated by medium-grained sand, but there were no differences in the soil texture at invaded and uninvaded sites. Similarly, knotweed has invaded sites with a range of slopes in multiple aspect directions with no slope or aspect being preferentially invaded. Japanese knotweed has invaded sites with limited shade qualities or with mainly deciduous trees, both of which may help with its growth. Inside patches, the percent carbon and nitrogen decreased, while 13C became more positive with increasing soil pH; these trends were not observed outside of the invaded patches. There was more Ca, K, Mg, Zn, and Mn available inside knotweed patches than outside of it. Once normalized for OM, no difference was found between these elements inside and outside of the patch, revealing that OM may be important in knotweed growth. Overall, it appeared that Japanese knotweed invasion is possible in a variety of physical settings and has no clear impact on a site’s physical characteristics but that it may alter a site’s biological and chemical properties

Hybridization in the invasive Fallopia complex and its influence on sexual reproduction and herbivore resistance

Biological invasions are considered to be an important cause of current biodiversity loss and can cause significant ecological problems. Several hypotheses have been proposed to explain why exotic plants become invasive. An important determinant of the success of invasive plants in their adventive range is the efficiency of reproduction. High fecundity and the potential for sexual reproduction, which generates genetic variability but also vigorous clonal growth, are attributes frequently observed among the most successful invasive plants. However, external factors also can influence plant invasions. One commonly accepted mechanism for the invasion success of plants is that plants introduced into a new range experience less herbivory due to the release from natural enemies resulting in higher plant fitness. Furthermore, biological invasions may be promoted by climate change. Altered environmental conditions due to climate change could be more favourable for many invasive species and could increase the reproduction, establishment and spread of exotic plants in the introduced range. Recently, it has been claimed that the ability of exotic plants to establish and rapidly expand in a novel range may also be shaped by evolutionary processes. Interspecific hybridization has been identified as a stimulus for the evolution of increased invasiveness in exotic plant species. Hybridization can increase genetic variation and provide the genetic material on which natural selection can act. Novel gene combinations may result in phenotypes that are stronger competitors, have higher reproduction and survival rates and are more resistant against herbivory and may therefore be favoured by natural selection. Moreover, hybridization may facilitate adaptation to different or altered environmental conditions, for example, due to climate change. Successful hybrid genotypes might be fixed and retained by vegetative propagation and increase the invasion success of exotic plants. Taxa of the genus Fallopia (Polygonaceae), native to eastern Asia, are among the most troublesome invasive species worldwide and are particularly aggressive in Europe and North America. The plants cause significant damage to native ecosystems and are especially a problem along rivers. In Europe, exotic Fallopia plants spread mainly by vegetative propagation. Of the widespread F. japonica var. japonica in Europe only a single genotype with male-sterile flowers has been found, and sexual reproduction in the exotic Fallopia complex is thus restricted mainly to hybridization among the taxa. The naturalized but less frequent species F. sachalinensis can act as pollen donor, resulting in the hybrid F. x bohemica. The hybrid is frequent and considered to have a higher invasion potential and a faster spread than its parental species. A third introduced species is the climbing F. baldschuanica. Hybridization between this species and F. japonica var. japonica results in the hybrid F. x conollyana, which so far has only rarely been reported from Europe. In my dissertation I present four studies on hybridization in the invasive Fallopia complex in Western Europe and its consequences. Specifically, I studied the genetic diversity and hybridization patterns (chapter 2), extent and variation in sexual reproduction (chapter 3), regional variation in seedling establishment and the potential effects of climate change (chapter 4) and the influence of hybridization on herbivore resistance (chapter 5)

ATR-FTIR Spectroscopy-Linked Chemometrics:A Novel Approach to the Analysis and Control of the Invasive Species Japanese Knotweed

Japanese knotweed (Reynoutria japonica), an invasive plant species, causes negative environmental and socio-economic impacts. A female clone in the United Kingdom, its extensive rhizome system enables rapid vegetative spread. Plasticity permits this species to occupy a broad geographic range and survive harsh abiotic conditions. It is notoriously difficult to control with traditional management strategies, which include repetitive herbicide application and costly carbon-intensive rhizome excavation. This problem is complicated by crossbreeding with the closely related species, Giant knotweed (Reynoutria sachalinensis), to give the more vigorous hybrid, Bohemian knotweed (Fallopia x Bohemica) which produces viable seed. These species, hybrids, and backcrosses form a morphologically similar complex known as Japanese knotweed ‘sensu lato’ and are often misidentified. The research herein explores the opportunities offered by advances in the application of attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy-linked chemometrics within plant sciences, for the identification and control of knotweed, to enhance our understanding of knotweed biology, and the potential of this technique. ATR-FTIR spectral profiles of Japanese knotweed leaf material and xylem sap samples, which include important biological absorptions due to lipids, proteins, carbohydrates, and nucleic acids, were used to: identify plants from different growing regions highlighting the plasticity of this clonal species; differentiate between related species and hybrids; and predict key physiological characteristics such as hormone concentrations and root water potential. Technical advances were made for the application of ATR-FTIR spectroscopy to plant science, including definition of the environmental factors that exert the most significant influence on spectral profiles, evaluation of sample preparation techniques, and identification of key wavenumbers for prediction of hormone concentrations and abiotic stress. The presented results cement the position of concatenated mid-infrared spectroscopy and machine learning as a powerful approach for the study of plant biology, extending its reach beyond the field of crop science to demonstrate a potential for the discrimination between and control of invasive plant species

Hybridization And Sexual Reproduction In The Invasive Alien Fallopia (Polygonaceae) Complex In Belgium

peer reviewed† Background and Aims The knotweed complex, Fallopia spp. (Polygonaceae), belongs to the most troublesome invasive species in Europe and North America. Vegetative regeneration is widely recognized as the main mode of reproduction in the adventive regions. However, the contribution of sexual reproduction to the success of these invasive species has only been detailed for the British Isles. An examination was made as to how hybridization may influence the sexual reproduction of the complex in Belgium and to determine how it may contribute to the dispersal of the species. † Methods Studies were made of floral biology, reproductive success, seed rain, seed bank, germination capacity, seedling survival and dispersal capacity in order to characterize the reproductive biology of the species. Moreover, chromosome counts and flow cytometry were used to assess the hybrid status of seedlings produced by sexual reproduction. † Key Results In the area investigated, extensive sexual reproduction by hybridization within the complex, including one horticultural species, was demonstrated. A small percentage of seeds may be dispersed outside the maternal clone (.16 m) allowing the formation of genetically differentiated individuals. Seed germination was possible even after a winter cold period. †Conclusions The extensive sexual reproduction by hybridization could further contribute to the dramatic invasive success of knotweeds in Belgium and should not be underestimated when considering control and management measures