Major emerging alien plants in Austrian crop fields

Globalisation and increasing trade have led to the introduction of alien plants that are highly competitive and difficult to control in agriculture in central Europe. Our study set out to analyse the invasion process and agricultural impact of the six emerging alien plants Abutilon theophrasti, Ambrosia artemisiifolia, Cyperus esculentus, Datura stramonium, Panicum schinzii and Sorghum halepense in Austria, based on a large distribution data set (694 occurrence records in crop fields). We found that all study species have increased in abundance and range, especially after the year 2000. The rate of spread was highest for A. artemisiifolia and lowest for C. esculentus. At present, records of the study species were largely associated with areas of high summer crop concentration in eastern, southern and north‐western Austria. Based on the CORINE land‐cover data set, we found that the agricultural area at risk of being invaded increased over time. At present, it ranges between 45 500 and 168 000 ha (approximately 2.4% and 8.7% of the total agricultural area) depending on the species. The invasion success of the study species is probably associated with frequent human‐mediated dispersal, specific crop‐dominated rotations and herbicide use. Our results suggest that the study species will successfully spread further. We conclude that these emerging alien species will cause substantial impacts on crops in Austria and probably in other countries of central Europe.     

Invasion process and potential spread of Amaranthus retroflexus in China

Amaranthus retroflexus, a troublesome agricultural weed native to North America, has expanded its distribution in large areas of China since its introduction around 1905. Geographical interpretation of changes in their distribution ranges could provide valuable insights on its spatiotemporal invasion patterns and could be used to predict the extent of its future spread. Based on compiled historical distribution occurrences of A. retroflexus in North American and Chinese ranges, invaded ecological niche models for three hypothetical invasion stages were developed. Native models on the basis of all available records within the North American range were also generated for reciprocal comparison with the invaded model. Climate similarity between native and invasive ranges was also investigated. Amaranthus retroflexus has exhibited a rapid and large range expansion after about a 50‐year lag, especially in central and western China. It established a relative stable distribution in the 1960s and has been undergoing a more continuous westward expansion since then. Presently A. retroflexus has not yet reached full occupancy of suitable habitats in China. The results highlight prioritising habitats in south‐western China for monitoring and control to prevent its further spread.     

Differences in growth and herbicide sensitivity among Cyperus esculentus clones found in Belgian maize fields

Cyperus esculentus is an invasive troublesome neophyte in many arable crops in Belgium. Applied weed control varies from field to field. One of the possible reasons for this variability might be a differential vegetative and reproductive behaviour among Belgian C. esculentus clones. In this study, growth characteristics and herbicide sensitivity of C. esculentus clones collected in Belgian maize (Zea mays) fields were evaluated. In a morphology Experiment, 25 clones were screened for growth characteristics and ability to set viable seeds under outdoor conditions. Dose – response experiments were conducted in the glasshouse to evaluate the effectiveness of two foliar‐applied herbicides (bentazon and glyphosate) and two pre‐sowing soil‐incorporated herbicides (S‐metolachlor and dimethenamid‐P) for controlling 14 C. esculentus clones. Response variables were aboveground dry biomass, tuber number, tuber dry biomass and individual tuber dry weight. Clones exhibited large differences in shoot number (up to 3.1‐fold), tuber dry biomass (up to 4.7‐fold), tuber number (up to 3.4‐fold), individual tuber dry weight (up to 4.8‐fold), inflorescence number and capacity to set viable seeds. Large interclonal differences in herbicide sensitivity (up to 8.3‐ and 4.0‐fold for aboveground dry biomass and tuber dry biomass, respectively) were observed. Contrary to foliar‐applied herbicides, soil‐incorporated herbicides were very effective and provided season‐long C. esculentus control at doses below the recommended maximum field dose. However, low doses stimulated tuber formation. Future C. esculentus management strategies should take into account differential growth characteristics and herbicide sensitivity of C. esculentus clones.     

Cyperus esculentus L. — A new weed in Israel

Cyperus esculentus L., a cosmopolitan noxious weed, has been recorded for the first time in an agricultural irrigated field in Israel. Hand-weeding, herbicides and soil disinfestation methods were only partially effective in controlling the weed. The distribution map of the weed is unknown, and it is unclear how the weed has been introduced into Israel. We estimate thatC. esculentus has a high risk potential to spread further and cause damage to Israeli agriculture, and therefore its spread should be restricted. http://www.phytoparasitica.org posting May 18, 2005.     

EFFECT OF MINIMUM SOIL TEMPERATURE ON DIFFERENTIAL DISTRIBUTION OF CYPERUS ROTUNDUS AND C. ESCULENTUS IN THE UNITED STATES*

Summary. The response of tubers to low temperatures was investigated to gain insight into a physiological basis for the differential distribution of Cyperus esculentus L. (yellow nutsedge) and C. rotundus L. (purple nutsedge) in the United States. Only C. esculentus tubers survived the winter of 1968–69 in the field at Urbana, Illinois. Less than 10% of C. rotundus tubers survived at 2°C for 12 weeks, whereas more than 95% of C. esculentus tubers survived this treatment. Exposures to -2°C for 4 h or longer killed 50% of C. rotundus tubers, whereas - 6·5°C was required to kill 50% of C esculentus tubers. C. rotundus distribution is restricted to regions where the soil seldom freezes, whereas C. esculentus is distributed in regions where the soil temperatures often get below freezing. Survival of C. esculentus tubers in soil which frequently freezes may account for its wide distribution. Death of C. rotundus tubers in soils which freeze apparently is the reason why the species is restricted to the southeastern and southwestern regions of the U.S.A. L'Influence de la température du sol sur la répartition différentielle de Cyperus rotundus et de Cyperus esculentus aux Etats-Unis     

Local spread of the invasive Cyperus esculentus (Cyperaceae) inferred using molecular genetic markers

Over the last 20 years Cyperus esculentus (yellow nutsedge) has become invasive in south‐west France. Because the genetic variation of invasive species can affect the success of management strategies, amplified fragment length polymorphism markers were used to assess the amount and distribution of genetic diversity in this clonally reproducing weed. Population samples of C. esculentus were collected mainly in south‐west France, with 21 samples of C. eragrostis also included in this study. A total of 113 polymorphic loci were identified (50% of the bands scored) in C. esculentus. A low level of genetic diversity (0.140) was detected, of which 95% were partitioned among sites. The regional patterns of variation could have been caused by rapid range expansion of clones propagated by harvesting machinery. Implications of the high clonality detected in C. esculentus are discussed in the context of the development of weed management strategies: because reproduction of the weed in Haute Lande occurs by tubers only, vegetable production should be reduced in infested areas.     

From horticulture and biofuel to invasion: the spread of Miscanthus taxa in the USA and Europe

Species of the genus Miscanthus (Poaceae) have recently become widely planted for ornamental and industrial uses. Yet these large perennial grasses have several traits that suggest a high invasion potential. To inform the debate on the benefits and risks of introducing these new biofuel crops, this publication summarises the invasion of Miscanthus species in Europe and the USA. Databases from North America were interrogated, and occurrence data from a variety of European sources were examined. In both continents, M. sinensis and M. sacchariflorus have recently spread rapidly, although invasion started earlier in the USA and both species are more widespread there. Both species mostly colonise grasslands and ruderal habitats. In addition, some escapes of the hybrid M. × giganteus, which has a particularly strong invasion potential because of its vigorous growth and greater capacity to establish in cool climates, have already been recorded. We conclude that the invasion potential of Miscanthus species needs to be thoroughly tested, the incipient invasions in Europe and the USA monitored and, if required, planting restrictions should be adopted.     

Crop rotation effects on Cyperus rotundus and C. esculentus population dynamics in southern California vegetable production

Control options for Cyperus rotundus and Cyperus esculentus (purple and yellow nutsedge) were evaluated within three cropping systems in the low desert of southern California: (1) standard vegetable crop rotation (weed‐free, uncontrolled nutsedge and cultivation) with spring cantaloupe (Cucumis melo) – summer fallow – winter broccoli (Brassica oleracea), (2) cover crop rotation (halosulfuron and smother crop) with spring wheat (Triticum aestivum)/corn (Zea mays) – summer sudangrass (Sorghum sudanense) – Winter Fallow, (3) rotation with solarization (non‐solarization and solarization) with spring wheat – summer fallow/solarization – winter broccoli. After two growing seasons, broccoli was planted without Cyperus control, to study the effect on yield. Cyperus rotundus tubers increased from 0.66 tubers per m² to 1260 tubers per m² in the uncontrolled treatment over two seasons. Cultivation during the growing season reduced C. rotundus tubers by 93% compared with the uncontrolled plots. Cover crop rotation did not reduce the number of C. rotundus tubers significantly, despite the dense sudangrass canopy shading the soil during most of the summer. Cyperus rotundus was effectively controlled by the solarization treatment. All methods controlled C. esculentus, especially when there were no crops growing in the summer. When broccoli was grown after two years of various management strategies, the cultivation treatment showed a 44% yield reduction compared with the weed‐free control, while the solarization treatment increased broccoli yield by 64% compared with the non‐solarization treatment. Rotations that included sudangrass had low broccoli yield when either C. rotundus or C. esculentus were present.     

Potential distribution of two Ambrosia species in China under projected climate change

The invasion of Ambrosia artemisiifolia and Ambrosia trifida from their native range to occupy large areas in China has raised considerable concern. Using the maximum entropy (Maxent) method, we developed models for each Ambrosia species, based on occurrence records from both native ranges (North America) and their invaded ranges (e.g. northern and south‐western Europe) to predict the availability and distribution of suitable habitats for these two species in China. For each species, we also assessed potential shifts in habitat suitability for the year 2050, using three general circulation models (GCMs) and two emission scenarios. Elevation and average mean precipitation in October contributed most to model development for both species. Potential distribution projections under future climatic change scenarios suggested an averaged percentage of suitable area (2.21%) and habitat gain (1.49%) in A. artemisiifolia distribution, with further expansion to environmentally favourable locations in south‐east coastal regions, northern Taiwan and the Beijing–Tianjin–Tangshan area in northern China. Future predicted percentage of suitable area for A. trifida was 0.03% with a very limited suitable habitat gain of <1% although this species had the potential to continue to spread in northern China. Our findings suggest that management priorities should be focused on A. artemisiifolia, whilst effective control strategies for A. trifida may be optimised by concentrating efforts on those relatively fewer regions of China where the species is currently abundant.     

Spread dynamics and agricultural impact of Sorghum halepense,an emerging invasive species in Central Europe

Sorghum halepense is a serious weed and reservoir for pathogens of crops worldwide that has recently spread in Austria. On the basis of an exhaustive distribution data set (302 records), we analysed the spread dynamics and agricultural impact. The first record of S. halepense was recorded in 1871, but the species remained rare until 1970. After a moderate increase in records until 1990, it has recently expanded strongly (>70% of all records have been collected since 1990), in particular, in the lowlands of eastern and southern Austria. Invasion into fields was first documented in the 1970s, but again, since 1990, S. halepense has spread strongly and fields now account for 32% of all records. In southern Austria, we found that S. halepense invasion already puts approximately 41% of grain maize fields and 40% of oil‐pumpkin fields at risk of yield losses. In cooler regions within Austria, S. halepense is still rarely recorded in fields. Sorghum halepense serves as a reservoir for the maize dwarf mosaic virus, as it was found in 38% of 21 samples collected in southern Austria. Invasion of S. halepense in fields was most likely assisted by frequent secondary dispersal and intensive maize and oil‐pumpkin cultivation. Given the fast and on‐going spread in fields, which is likely to continue under climate warming, our results provide evidence that S. halepense will cause serious impacts for agriculture in Austria and probably in other countries of Central Europe.     

Host specificity of Puccinia canaliculata,a potential biocontrol agent for Cyperus esculentus

Aim was to clarify the rust fungusPuccinia canaliculata for release in a new environment where it may be utilized as a microbial herbicide. A strain of the rust was introduced from the USA into the Netherlands and kept in quarantaine. The susceptibility ofCyperus esculentus and several other species of the Cyperaceae was tested. C. esculentus leptostachyus from five locations was susceptible toP. canaliculata. C. esculentus of a yet unidentified biotype from two locations was moderately susceptible (fewer and smaller pustules than on leptostachyus), whereas plants of the same biotype from a third location were resistant to the rust.C. esculentus esculentus (from one location) andC. esculentus sativus (a crop) were also resistant to the rust. C. albostriatus, C. alternifolius, C. flavescens, C. rotundus, Carex hirta, Eleocharis palustris, andScirpus maritimus were resistant toP. canaliculata. OnCyperus fuscus, P. canaliculata produced very small urediniosori (less then 1 mm in diameter); the sori were surrounded by a zone of necrotic plant tissue.From the observations onC. fuscus we concluded that the (potential) host range ofP. canaliculata is wider than we originally expected. For safety reasons, it was decided not to release it in the Netherlands.     

Patterns of loss of biodiversity associated with invasion by Chrysanthemoides monilifera subsp. monilifera (boneseed) across a large geographic region

To investigate the impact of invasion by Chrysanthemoides monilifera ssp. monilifera (boneseed) on plant communities, sites that were invaded and uninvaded were surveyed across Tasmania, South Australia and Victoria, Australia. Above‐ground cover abundance was estimated and samples of the seed bank from invaded and uninvaded sites in each state were collected and germinated in the glasshouse. We compared species richness and composition between invaded and uninvaded sites for both above‐ground and below‐ground samples. Across this broad geographic area, C. monilifera invaded sites had 25% fewer species than uninvaded sites and twice as many exotic species. Most growth forms showed reduced richness in invaded sites. There were no differences in the composition of native species communities between invaded and uninvaded sites in most regions, except South Australia. The composition of the seed bank differed from the above‐ground vegetation, but was similar within each state. Herbs and grasses were most abundant. The species composition of the seed bank was different in invaded sites only in Victoria, suggesting that invasion may negatively influence the capacity of the seed bank to restore vegetation in some areas. However, the underlying mechanisms for the observed patterns were not tested in this study. The capacity of all sites to regenerate effectively from the seed bank was limited and, in order to ensure the conservation of biodiversity into the future, monitoring of species richness at smaller scales, particularly those where management of C. monilifera has occurred, will be needed to ensure management can facilitate the establishment of missing species. This study suggests that C. monilifera impacts a range of functional groups and different species across its distribution and is therefore non‐selective in how it influences changes in communities.     

Parthenium hysterophorus in Nepal: a review of its weed status and possibilities for management

The rapid expansion of the alien invasive Parthenium hysterophorus is a new agricultural and environmental problem for Nepal. Although the weed was first recorded in 1967, the most significant expansion has occurred in the last 20 years. The weed is thought to have entered Nepal from India and currently is found in the Tarai, Siwalik and hill regions of Nepal. A CLIMEX modelling projection has shown these regions to be climatically suitable for the growth of P. hysterophorus, both under the present and a future projected increased temperature. From the initially invaded roadside vegetation, the weed has now spread into cropping land and forests. Vehicle movement and transportation of agriculture products are the main means by which its seed is spreading. The weed has reduced plant species richness and changed species composition in grasslands, while fodder collectors have developed contact dermatitis from the plant. To date, no sustainable management strategy has been developed for this weed. However, the fortuitous arrival of the biological control agents Zygogramma bicolorata and Puccinia abrupta var. partheniicola has had some impact upon the weed's growth and abundance. A CLIMEX modelling projection identifies many suitable locations for Z. bicolorata outside of its present range and within areas where the weed is likely to spread, both under the present and under a future projected climate of increased temperature. Mapping of the currently invaded areas, management through community involvement and further releases of new and redistribution of current biological control agents are required to manage P. hysterophorus in Nepal.     

Genetic variation and structure in native and invasive Solidago canadensis populations

Solidago canadensis is native to North America, but has become a noxious invasive plant in China. We know only a little about its invasion history and the effects of introductions on its genetic composition. Here, we investigated genetic variation and structure between 15 North American and 13 Chinese populations of S. canadensis using AFLP makers. Four AFLP loci suggested relatively high genetic diversity of this weed and similar genetic variation between the invasive range and the native range. Most genetic variation was within populations across two ranges, but the Chinese range had a higher degree of among‐population variation than the North American range. Multiple tests, including Bayesian assignment, UPGMA analysis, PCoA and analysis of ‘isolation by distance’, showed that the Chinese populations originated from at least two distinct native sources and that secondary introduction or dispersal should be common in China. Also, North American populations were possibly a single genetic group. Overall, S. canadensis in China was probably founded from multiple introductions and then spread through long‐distance dispersal associated with human activities. Genetic variability in the species in the invaded range appears to have favoured establishment and spread and may well provide a challenge to successful control.     

Reduction of growth and reproduction of Cyperus esculentus by specific crops

To assess the potential contribution of growing highly competitive crops to control Cyperus esculentus in the Netherlands, the influence of silage maize, hemp, winter barley and silage winter rye on emergence, growth and reproduction of this weed was studied in two field experiments. Growth and reproduction of C. esculentus (determined both as tuber production per plant and density of the weed in the subseuent crop maize) was reduced by each crop, compared to plots in which no crop was grown. In hemp, hardly any tuber production was observed. By growing a green manure crop after harvest of the winter barley the tuber production of the weed was reduced to about 40% of that in winter barley followed by fallow. Decreasing the light regime in a greenhouse experiment in the same order as was observed in the crops winter barley, maize and hemp, caused a similar reduction of tuber production to that found in the field. Therefore, it is suggested that competition for light is the main factor explaining the observed crop effects on the population dynamics of the weed. It is concluded that growing competitive crops as hemp in rotation may effectively complement chemical control of C. esculentus.     

警惕危险性害虫辣椒花象甲入侵我国

辣椒花象甲Anthonomus eugenii是一种毁灭性害虫,原产于中美洲,可为害至少35种商业辣椒品种,对辣椒为害严重,可使其减产33%～90%。该害虫于1993年入侵加拿大,并于2014年进入欧洲。频繁的全球贸易及国际运输将加速该害虫的传播和扩散,并有入侵我国的风险。该文对辣椒花象甲的生物学特性、寄主植物、为害特征、分布范围及传播进行总结,分析其对我国的入侵风险及对我国辣椒产业造成的潜在损失,并提出风险管理措施。     

基于MAXENT的稻水象甲在中国的入侵扩散动态及适生性分析

稻水象甲Lissorhoptrus oryzophilus Kuschel是中国水稻上的重要植物检疫性害虫,根据稻水象甲的分布数据及其主要寄主水稻的分布,利用MAXENT生态位模型和ArcGIS对其在中国的入侵扩散动态及适生性进行了再分析和预测。稻水象甲在中国的扩散主要分为2个阶段:1988—1996年为零星扩散阶段,稻水象甲分布集中在环渤海湾及东南沿海地区,首次入侵发现地大多出现在港口城市;2001年至今为快速扩散阶段,稻水象甲逐步从沿海地区向内陆省份扩散,首次入侵发现地大多位于铁路或公路沿线城市。稻水象甲在中国的适生区广泛,90%以上水稻种植区均适合其生存,高度适生区域主要集中分布在南方稻区,少量分布在环渤海湾一带。     

Distribution of Parthenium hysterophorus and one of its biological control agents (Coleoptera: Zygogramma bicolorata) in Nepal

Parthenium hysterophorus is a noxious invasive weed of both agricultural and natural ecosystems, spreading aggressively in Nepal. Management of this weed in Nepal has been limited, mainly because of the lack of geo‐referenced data concerning the weed's distribution. We conducted a nationwide survey of P. hysterophorus and its coleopteran biological control agent Zygogramma bicolorata from 2013 to 2016 to determine their spatial distribution. Both were widespread, with the distribution of Z. bicolorata lagging behind the invasion front of P. hysterophorus. The weed was present in 21.2% of the 4838 locations examined, including several isolated satellite populations. The weed was found in the Tarai, Siwalik, Middle Mountains and High Mountains regions, reaching up to 2000 m asl. It has invaded natural and modified ecosystems including all six protected areas in the Tarai and Siwalik regions. Road access appears to be the major pathway for its long‐distance dispersal. Zygogramma bicolorata had spread from the east to the west and was present in 15.4% of the weed occurrence locations, inflicting a low amount of damage. A CLIMEX modelling projection revealed the presence of additional geographic areas in Nepal which are climatically suitable for both P. hysterophorus and Z. bicolorata. Eradication of satellite populations of the weed by physical and chemical measures, and the release of Z. bicolorata into new, but climatically suitable, locations should be prioritised for P. hysterophorus management in Nepal. In conclusion, P. hysterophorus has rapidly become widespread in Nepal and the currently available biological control agent has not been able to prevent further spread of the weed.     

Effect of anaerobic soil disinfestation amendment type and C:N ratio on Cyperus esculentus tuber sprouting,growth and reproduction

Anaerobic soil disinfestation (ASD) is a cultural technique primarily targeted for control of soilborne plant pathogens, but can also impact weed propagules. A repeated pot study was conducted to evaluate ASD treatment impact on sprouting and growth of introduced Cyperus esculentus (yellow nutsedge) tubers using dry molasses‐based and wheat bran‐based amendment mixtures at four carbon‐to‐nitrogen (C:N) ratios (from 10:1 to 40:1) and compared with a non‐amended control. The mean percentage of sprouted tubers recovered after ASD treatment was lower for wheat bran‐based (42%) than dry molasses‐based (65%) amendments, and tuber production was 1.6‐fold higher in dry molasses‐based than wheat bran‐based treatments. The highest percentage of sprouted tubers (79%) and the highest mean production of large tubers (threefold higher than wheat bran‐based and 1.7‐fold higher than molasses‐based amendments) were observed for the non‐amended control. Tuber sprouting was significantly lower from all ASD treatments (regardless of amendment C:N ratio) compared with the non‐amended control at a 15 cm burial depth. New tuber production was lowest at C:N ratios of 10:1 and 20:1 and more than twofold higher in the non‐amended control. Wheat bran‐based amendments reduced above‐ground C. esculentus biomass compared with the non‐amended control and ASD treatments with molasses‐based amendments, and reduced below‐ground biomass compared with molasses‐based amendments. Above‐ground biomass was highest at amendment C:N ratio of 10:1, and below‐ground biomass was highest at amendment C:N ratio of 40:1 and the non‐amended control. ASD treatment with wheat bran‐based amendments at lower C:N ratios reduced tuber sprouting and reproduction compared with the non‐amended control, but not at rates high enough to use as a primary weed management tactic.     

Biology and management of the invasive weed Ageratina adenophora (Asteraceae): current state of knowledge and future research needs

Biological invasion is increasing worldwide and the management of invasive species is becoming an important priority for vegetation managers. Success of invasive species management depends on a thorough understanding of the biology of the organism in question and the effectiveness of current management efforts, in order to identify the best practices for management improvement. In this review, we synthesised current biological knowledge of a noxious invasive weed Ageratina adenophora to identify knowledge gaps and assessed management efforts to identify best practices. Finally, we proposed some priority areas for future research to fill knowledge gaps and improve management. Our analysis showed that A. adenophora has already invaded 40 countries, mainly in Asia, Oceania, Africa and Europe. Phenotypic plasticity, allelopathic interference and invasion‐mediated changes in the soil microbial community are the proposed mechanisms that facilitate rapid spread of this weed. However, allelopathy as a mechanism of invasion success of this weed has not been supported by ecologically meaningful experiments. Though mechanical, chemical and biological control measures have been used, their success remains limited and the weed continues to spread in new regions. Among seven biological control agents examined to date, gall fly (Procecidochares utilis) and leaf spot fungus (Passalora ageratinae) have been effective in limited areas to suppress growth of this weed. Some perennial native grasses (e.g. Setaria sphacellata and Lolium perenne) have shown potential to competitively suppress A. adenophora. In conclusion, understanding the invasion mechanisms, exploring further to identify effective biological control agents, combined with approaches of ecological restoration, could help in the management of this weed.