Wintering of the biotrophic fungus Puccinia lagenophorae within the annual plant Senecio vulgaris: implications for biological weed control

Epidemics of the obligate biotrophic fungus Puccinia lagenophorae might be used to control populations of the annual plant, groundsel, Senecio vulgaris . Insight into the mechanisms of survival of P. lagenophorae over winter may help to explain the number of inoculum sources, and their strength (assessed by number and size of pustules), present in an S. vulgaris population in spring, indicating the probability and rate of progress of a subsequent epidemic. Results of the study indicated survival of the rust as mycelium within the host over winter. Survival outside the host is unlikely, because aecidiospores lost their capacity to germinate over winter and teliospores have not been reported to be infectious. Survival of S. vulgaris plants over winter was reduced by rust infection in autumn. The mortality of S. vulgaris was 30–100% depending on the date of infection. All plants infected early in autumn died but those infected late in autumn were more likely to survive. In turn, poor survival of the host impacted on the survival of P. lagenophorae over winter. Consequently, the results of the study suggest that no inoculum sources, or only a few weak ones, are present in vulgaris populations in spring. This suggestion was supported by observations of an S. vulgaris population at a ruderal site. Therefore, research on biological weed control should focus on increasing the negative impact of P. lagenophorae on S. vulgaris populations while augmenting the probability of survival of the rust over winter to start new epidemics in spring.     

Crab apple blossoms as a model for research on biological control of fire blight

ABSTRACT Nonseasonal availability of pomaceous flowers could improve laboratory detection and prefield testing of biocontrol agents for fire blight of pear and apple. Crab apple was selected as a model because of its high flower productivity on 1-year-old wood, high susceptibility to fire blight, and availability from nurseries. Cultivars Manchurian and Snowdrift were manipulated to bloom once by transferring dormant nursery trees from a cold room to a greenhouse and a second time by defoliating trees and applying 1% cytokinin and 0.1% gibberellins to the buds with a brush. Different sets of trees were induced at different times to bloom, so that flowers were produced 12 months in the year. When known bacterial antagonists (Erwinia herbicola strain C9-1 and Pseudomonas fluorescens strain A506) were applied alone or in combination to the stigmas of detached crab apple blossoms prior to inoculation with the pathogen (E. amylovora strain Ea153), population interactions over time were comparable to those reported in previous studies involving pear or apple. In a subsequent series of experiments, the relative effects of 12 bacterial strains on stigmatic populations of strain Ea153 were similar for detached blossoms of crab apple in the laboratory, blossoms of intact crab apple trees in the greenhouse, and blossoms of pear and apple in the field. Additionally, when stigmas of detached crab apple blossoms were inoculated with antagonists (strains C9-1 and A506) and the pathogen, and later subjected to a 24-h wetting period, bacterial populations in the flower hypanthium increased and disease was suppressed. These studies indicate that crab apple blossoms can serve as a suitable model for year-round evaluation and study of biocontrol agents for fire blight.     

Mulched cover crops as an alternative to conventional weed management systems in vineyards

Conventional methods of weed management in vineyards rely primarily on herbicides and tillage. The desire to adopt alternatives to these methods is driven by environmental and economic reasons. Weed suppression and grape yield under mulched cover crop systems at two rainfed northern California vineyards were similar to, and at times exceeded, those under conventional tillage or herbicide management. Cover crop productivity was positively correlated with weed suppression and mulch decomposition rates and seemed to be determined primarily by location and then by cover crop type. The mulch from mowed cover crops averaged 603(± 94) gm⁻² at the two sites. Weed suppression was linked to light interception by the mulch cover for most weed species. Subterranean clover planted directly in the vine row significantly reduced weed cover where it established. The increased dominance of the perennial Convolvulus arvensis and reduction of certain annual species was indicative of species compositional changes in all treatments. Profits under the cover cropping systems exceeded those under conventional tillage and herbicide systems by €  794 ha⁻¹ averaged over the duration of the experiment at both locations.     

Using plant population biology in weed research: a strategy to improve weed management

The aim of this paper is to show the need for developing plant population biology studies in order to improve weed management when traditional approaches in weed science have failed, as shown by recent reviews on herbicide resistance. It is also suggested that the usual weed definitions do not reflect the new aims of weed ecology. The results of studies on the genetic, demographic and spatial variability of weed populations and their regulation by pests and pathogens are reported, and are discussed in the specific case of clonal perennial species.     

Constraints in implementing biological weed control: A review

Biological weed control is a selective, environment-friendly process, utilizing host-specific control agents towards targeted weeds that prevent damage to non-target crops or native plants. The objective of biological control for weeds is not to eradicate but, rather, to regulate weed populations below levels that cause economic injury. There has been criticism that biological weed control research efforts aim to substitute one purchased input (a bioherbicide) for another (a chemical herbicide). It is essential to remember that 'bioherbicides' and 'biological weed control' are not synonymous. Biological control of weeds involves using any organism to reduce or eliminate the detrimental effects of weed populations, whereas bioherbicides utilize plant pathogens repeatedly. The integration of herbicides, both chemical and biological, into ecologically based weed management is an essential process for the sustainability of agriculture. Throughout this review, the constraints affecting the implementation of biological weed control are described. Greater understanding of the morphology, phenology and genetic diversity of targeted weeds is emphasized and the need to examine all aspects related to biocontrol agents is stressed. Improved technologies, better public support and financial aid, and more scientific interest, will all contribute to the progress of the 'science of biological weed control'.     

Practical experiences with a system for site-specific weed control in arable crops using real-time image analysis and GPS-controlled patch spraying

Information on temporal and spatial variation in weed seedling populations within agricultural fields is very important for weed population assessment and management. Primarily, spatial information allows a potential reduction in herbicide use, when post‐emergent herbicides are only applied to field sections with high weed infestation levels. This paper presents a system for site‐specific weed control in sugar beet, maize, winter wheat, winter barley, winter rape and spring barley. The system includes on‐line weed detection using digital image analysis, computer‐based decision making and Global Positioning System‐controlled patch spraying. In a 2‐year study, herbicide use with this map‐based approach was reduced in winter cereals by 6–81% for herbicides against broad leaved weeds and 20–79% for grass weed herbicides. Highest savings were achieved in cereals followed by sugar beet, maize and winter rape. The efficacy of weed control varied from 85% to 98%, indicating that site‐specific weed management will not result in higher infestation levels in the following crops.     

Punch planting, flame weeding and stale seedbed for weed control in row crops

Punch planting is introduced as a new method to reduce weeds within rows in organically grown crops. In this method a hole is punched in the soil, and a seed is dropped into it, without seedbed preparation and soil disturbance outside the hole. In 2 years, punch planting with flame weeding, normal planting with flame weeding and normal planting without flame weeding were compared in fodder beet for five planting dates. Each planting date represented a lag‐period since establishment of the stale seedbed. Over all planting times and years, punch planting with flame weeding reduced intra‐row weed densities by 30% at the two to four leaf stage of fodder beet compared with normal drilling with flame weeding. Punch planting with flame weeding also reduced intra‐row weed densities by 50% compared with normal drilling without flame weeding. In general, there was no improved performance of punch planting with flame weeding over years by later planting, but delayed planting reduced intra‐row weed densities significantly. Over 2 years, 240 day degrees Celsius (4 weeks) planting delay reduced intra‐row weed densities in the range of 68–86% depending on plant establishment procedure. Punch planting with flame weeding offers a promising method of weed control in organic farming.     

Reducing intrarow weed numbers in row crops by means of a biennial cultivation system

Intrarow weed emergence in row crops can be reduced by means of a biennial cultivation system that is based on an exhaustion of the weed seedbank in the upper soil layer of crop‐free bands established in a preceding cereal crop, year I, before the row crop, year II. In this study, a series of field experiments is presented focusing more specifically on the influence of prevention of weed seed shedding and of different cultivation tactics in the system on intrarow weed emergence in the bands in year II. As the system excludes inverting soil tillage between years I and II, the prevention of weed seed shedding in year I turned out to be a key factor in achieving the desired effect of the system. This was seen with spring barley grown in year I, but not with winter wheat, where the system actually resulted in an increase in intrarow weed numbers in spite of the measures taken in year I. Cultivating the crop‐free bands in spring barley in year I with conventional goose‐foot shares in order to enhance seed germination and mortality further had no significant effects regardless of time and intensity. Results from two other experiments, in which freshly shed weed seeds were incorporated into the soil, supported the finding that cultivating the bands was of no advantage.     

Glyphosate-resistant soybean as a weed management tool: Opportunities and challenges

Transgenic soybean, resistant to glyphosate, represents a revolutionary breakthrough in weed control technology. Transgenic soybean is the most dominant among all transgenic crops grown commercially in the world. In 2000, glyphosate-resistant (GR) soybean was planted to 25.8 million hectares globally, which amounts to 58% of the total global transgenic crop area. The United States soybean area planted with GR soybean has increased from 2% in 1996 to 68% in 2001. Glyphosate-resistant soybean as a weed management tool has provided farmers with the opportunity and flexibility to manage a broad spectrum of weeds. The use of glyphosate in GR soybean offers another alternative to manage weeds that are resistant to other herbicides. The rapid increase in GR soybean area is caused by the simplicity of using only one herbicide and a lower cost for weed control. Adoption of GR soybean has resulted in a dramatic decrease in the area treated with other herbicides. Glyphosphate-resistant soybean should not be relied on solely to the exclusion of other weed control methods, and should be used within integrated weed management systems. Over-reliance on GR soybean could lead to problems such as shifts in weed species and population, and the development of glyphosate-resistant weeds. The challenge is for soybean farmers to understand these problems, and for weed scientists to communicate with farmers that continuous use of glyphosate may diminish the opportunity of GR soybean as a weed management tool in the future.     

Reviewing research priorities in weed ecology,evolution and management: a horizon scan

Weedy plants pose a major threat to food security, biodiversity, ecosystem services and consequently to human health and wellbeing. However, many currently used weed management approaches are increasingly unsustainable. To address this knowledge and practice gap, in June 2014, 35 weed and invasion ecologists, weed scientists, evolutionary biologists and social scientists convened a workshop to explore current and future perspectives and approaches in weed ecology and management. A horizon scanning exercise ranked a list of 124 pre‐submitted questions to identify a priority list of 30 questions. These questions are discussed under seven themed headings that represent areas for renewed and emerging focus for the disciplines of weed research and practice. The themed areas considered the need for transdisciplinarity, increased adoption of integrated weed management and agroecological approaches, better understanding of weed evolution, climate change, weed invasiveness and finally, disciplinary challenges for weed science. Almost all the challenges identified rested on the need for continued efforts to diversify and integrate agroecological, socio‐economic and technological approaches in weed management. These challenges are not newly conceived, though their continued prominence as research priorities highlights an ongoing intransigence that must be addressed through a more system‐oriented and transdisciplinary research agenda that seeks an embedded integration of public and private research approaches. This horizon scanning exercise thus set out the building blocks needed for future weed management research and practice; however, the challenge ahead is to identify effective ways in which sufficient research and implementation efforts can be directed towards these needs.     

Weeds for weed control: Asteraceae essential oils as natural herbicides

The aim of this study was to test the botanical family of Asteraceae as a source of natural herbicides. Twenty Asteraceae species were collected during flowering time and evaluated in terms of the yield and quality of essential oils (germination inhibition and growth of weeds). Half the species showed a sufficient yield of essential oil (from about 0.1% to 1.43%) when testing these phytochemicals in vitro as germination inhibitors of two typical weeds, Amaranthus retroflexus and Setaria viridis. Despite the higher tolerance of S. viridis, the concentration of 100 μg L^?1 of essential oils of the two Artemisia species and Xanthium strumarium could totally inhibit germination. In addition, at 10 μg L ^?1, the same essential oils showed full inhibition of A. retroflexus seeds. A comparison of their effectiveness at suboptimal doses led to a further selection of the most promising sources of essential oils. After their chemical characterisation, the essential oils were tested as post‐emergence herbicides on seedlings of the above‐cited weeds. After spraying the weeds at different concentrations (10, 100 and 1000 mg L^?1) during two different phenological stages of weed seedlings (cotyledons and the third true leaf), the essential oils of Artemisia annua and X. strumarium showed the best performance. The essential oils of X. strumarium were then tested again on both weeds to monitor the dynamics of plant injury. A reduction in plant fresh weight (about 20%–30% after 10 days) and chlorophyll content (destroyed, after the same amount of time) was found, thus confirming the total and rapid effectiveness of these essential oils. In summary, A. annua and X. strumarium have elicited considerable agronomic interest and appear to be suitable as a source of essential oils to act as natural herbicides.     

Combining physical, cultural and biological methods: prospects for integrated non-chemical weed management strategies

Physical, cultural and biological methods for weed control have developed largely independently and are often concerned with weed control in different systems: physical and cultural control in annual crops and biocontrol in extensive grasslands. We discuss the strengths and limitations of four physical and cultural methods for weed control: mechanical, thermal, cutting, and intercropping, and the advantages and disadvantages of combining biological control with them. These physical and cultural control methods may increase soil nitrogen levels and alter microclimate at soil level; this may be of benefit to biocontrol agents, although physical disturbance to the soil and plant damage may be detrimental. Some weeds escape control by these methods; we suggest that these weeds may be controlled by biocontrol agents. It will be easiest to combine biological control with fire and cutting in grasslands; within arable systems it would be most promising to combine biological control (especially using seed predators and foliar pathogens) with cover‐cropping, and mechanical weeding combined with foliar bacterial and possibly foliar fungal pathogens. We stress the need to consider the timing of application of combined control methods in order to cause least damage to the biocontrol agent, along with maximum damage to the weed and to consider the wider implications of these different weed control methods.     

Using phenology prediction in weed management: a review

The success of weed management based on ecological principles and weed biology will depend on a better understanding of the effect of environment on lift history strategies, growth, and competition of weeds; and crops, and particularly upon the ability to predict weed and crop phenology, This paper reviews the importance of phenotypic plasticity to weed and crop competition and other biological interactions. We also discuss the utility of phenological predictions in weed management and review current weed phenology models that are based on thermal time. By understanding the variables that drive plant phenotypic responses, new approaches and more long-term solutions for weed problems can be developed.     

Challenges facing arthropod biological control: identifying traits for genetic improvement of predators in protected crops

Biological control is an efficient pest control method but there are still limitations that are hindering its wider adoption. Genetic improvement of biological control agents (BCAs) can help to overcome these constraints, but the choice of key attributes for better performance that need to be selected is still an open question. Several characteristics have been suggested but the harsh reality is that selective breeding of BCAs has received a lot of attention but resulted in very little progress. Identifying the appropriate traits to be prioritized may be the first step to reverse this situation. In our opinion, the best way is to look at the factors limiting the performance of key BCAs, especially generalist predators (pesticide compatibility, prey‐density dependence, non‐suitable crops, and extreme environmental conditions), and according to these challenges, to choose the attributes that would allow BCAs to overcome those limitations. The benefits of selection for higher resistance to toxins, whether artificially applied (pesticides) or plant produced (plant defenses); increased fitness when feeding on non‐prey food (supplemented or plant‐derived); and better adaptation to extreme temperature and humidity are discussed. In conclusion, genetic improvement of BCAs can bring about new opportunities to biocontrol industry and users to enhance biocontrol resilience. © 2020 Society of Chemical Industry     

A European weed survey in 10 major crop systems to identify targets for biological control

In 1986, the Working Group on Biological Control within the European Weed Research Society planned a weed survey in 10 major crop systems throughout Europe. They were: (1) winter and (2) spring cereals, (3) maize and sorghum, (4) potatoes, (5) sunflower and soya, (6) colza (winter rapeseed), (9) sugar beet and (10) temperate orchards and irrigated Mediterranean orchards. Questionnaires were sent out to prominent weed scientists in all 26 European countries to rate the abundance and frequency of important weeds according to three classes for all crop systems in their respective countries. The results of the survey are presented. Based on the per cent of maximum score attained by individual weed species the 15 most important weeds were determined for each crop, and the 20 top scoring weeds for all crop systems combined. The prospects for biological control of weeds in Europe are discussed. Etude européenne des mauvaises herbes de dix cultures majeure.s en vue d'identifier les possi-bilités de lutte biologique En 1986, le Groupe de travail sur la lutte biologique au sein de la Société Europeenne de Mal-herbologie (European Weed Research Society) a organisé une enquete sur les mauvaises herbes présentes dans dix cultures majeures d'Europe: (1) céréales d'hiver et (2) d'été, (3) maïs et sorgho, (4) pomme de terre, (5) tournesol et soja, (6) colza, (7) cultures légumières, (8) vignes et verges méditerranéens non irrigués, (9) bet-terave à sucre et (10) vergers de la zone tem-pérées et méditerranéens irrigués. Des questionnaires ont été envoyés à des mal-herbologues reconnus des 26 pays européens pour, au moyen d'une classification à trois niveaux, évaluer dans leur pays 1'abondance et la fréquence des mauvaises herbes importantes dans ces systèmes de culture. Les résultats de 1'enquête sont présentés. Les 15 mauvaises herbes les plus importantes ont été déterminées pourchaque culture en fonc-tion du pourcentage du score maximum atteint par les différentes espèces, ainsi que les 20 mauvaises herbes obtenant les plus haul scores pour toutes les cultures combinées. Les possibilités de lutte biologique centre les mauvaises herbes en Europe sont discutees. Erhebung über die Verbreitung europäischer Unkrautarten als mögliche Zielefiir eine biologis-che Bekämpfung in zehn Hattptkultiiren Die Arbeitsgruppe ‘Biologische Bekämpfung’ der Europäischen Gesellschaft für Herbologie plante 1986 eine Unkrautaufnahme in 10 großen Kulturen in ganz Europa: (1) Wintergetreide. (2) Sommergetreide, (3) Mais und Sorghum, (4) Kartoffel, (5) Sonnenblume und Soja, (6) Winterraps, (7) Gemüse, (8) Wein und nichtbewässerte mediterrane Obstkulturen, (9) Zuckerrübe und (10) mitteleuropäische und bewässerte mediterrane Obstkulturen. Das Ergebnis einer Umfrage in allen 26 europäischen Ländern über die Abundanz und Frequenz wichtiger Unkräuter wird dargestellt. Die 15 für jede Kultur wichtigsten Arten und die 20 allgemein häufigsten Arten wurden bestimmt. Die Möglichkeiten der biologischen Unkrautbekämpfung in Europa werden diskutiert.     

Biological control of weeds in crops: a coordinated European research programme (COST-816)

For dominant weed species that are difficult to control by traditional means, the development of new, selective, control methods that can be implemented in integrated pest management (IPM) is essential. Here, biological control can be the appropriate means of control due to its high degree of selectivity and environmental safety (direct control value). The biocontrol strategy is based on a detailed analysis of the crop environment and, thus, provides a fundamental tool for developing sustainable agroecosystems (indirect, heuristic value). The successful application of biological weed control will lead to substantial reductions in pesticide use and, thus, will also contribute to the conservation, augmentation and utilization of biodiversity in agroecosystems, an explicit objective of IPM. Only cooperative and concerted efforts, such as those envisaged by COST, will allow the effective completion of weed biocontrol projects within a reasonable period of time. At present, over 25 institutions from 14 countries are participating in this COST action. The following six objectives have been defined for COST-816: to bring together European institutions, to promote a programme for scientific research and exchange, to draw up a general protocol for biological weed control in Europe, to integrate biological control into general weed management strategies, to establish a protocol to resolve potential conflicts of interest and to establish a list of agricultural weed species in Europe for biological control. Three principal methods of biological weed control are used in COST-816: the inoculative or classical approach, the system management approach and the inundative or microbial herbicide approach. Initially, Amaranthus spp., Convolvulus arvensis/Calystegia sepium, Chenopodium album and Senecio vulgaris were chosen as target weeds, each being the subject of a working group. A fifth working group on the control of Orobanche spp. control is in preparation. This concentration on a few target weed species has greatly stimulated cooperation and facilitated technology transfer between the research groups     

A review of the potential for competitive cereal cultivars as a tool in integrated weed management

Competitive crop cultivars offer a potentially cheap option to include in integrated weed management strategies (IWM). Although cultivars with high competitive potential have been identified amongst cereal crops, competitiveness has not traditionally been considered a priority for breeding or farmer cultivar choice. The challenge of managing herbicide‐resistant weed populations has, however, renewed interest in cultural weed control options, including competitive cultivars. We evaluated the current understanding of the traits that explain variability in competitive ability between cultivars, the relationship between suppression of weed neighbours and tolerance of their presence and the existence of trade‐offs between competitive ability and yield in weed‐free scenarios. A large number of relationships between competitive ability and plant traits have been reported in the literature, including plant height, speed of development, canopy architecture and partitioning of resources. There is uncertainty over the relationship between suppressive ability and tolerance, although tolerance is a less stable trait over seasons and locations. To realise the potential of competitive crop cultivars as a tool in IWM, a quick and simple‐to‐use protocol for assessing the competitive potential of new cultivars is required; it is likely that this will not be based on a single trait, but will need to capture the combined effect of multiple traits. A way needs to be found to make this information accessible to farmers, so that competitive cultivars can be better integrated into their weed control programmes.     

Audiotex system for monitoring and control of pests in field crops1

A telephone-based interactive voice response system (audiotex) integrated to a relational database has been implemented in Denmark for monitoring and control of pests in spring barley, winter barley, winter wheat, field pea and sugar beet. The system has been implemented using Powerline II Voice Response System and Inforniix-SQL RDBMS on a Commodore 486–25C PC under MS-DOS 5.0. The system is programmed in Microsoft C Version 6.0 with Informix ESQL/C Version 2.10 and Powerline II C Commando Version 1.2 programming interfaces. The database contains information pertaining to the farmer, the agronomic conditions of the field, individual field observations, recommendation model constants and the weather data. The user enters the field observations using a touch-tone telephone and prerecorded messages are used to guide the user during the data entry and for advising control measures. From the beginning of June to the end of July 1992, 129 farmers with 486 fields were offered the audiotex service. Usability analysis of the system showed that the system was simple to use and provided timely advice on control measures. Farmers indicated that they would continue to use the audiotex. Compared to an earlier recommendation service, which required 24–36 h for control recommendations to reach the farmers through postal services, the audiotex provides control recommendations immediately after data entry on the telephone.     

Can an integrated management approach provide a basis for long-term prevention of weed dominance in Australian pasture systems?

Broad-leaved weeds in pasture, such as Carduus nutans, Onopordum spp. and Echium plantagineum are a major problem for graziers in southern Australia. Previous attempts to combat these weeds with a single technique have only resulted in short-term success. An approach to long-term control, combining biological control with different grazing and herbicide strategies, was evaluated in an integrated weed management (IWM) programme, in south-eastern Australia. This IWM study was one of the few that has focused on biological control agents. During the field trials, the impacts of grazing and herbicide treatments on the weed and biological control agents, as well as on pasture composition, were monitored. This paper concentrates on the part of the study that focuses on the role and importance of pasture composition as part of weed management. The main pasture components were monitored using botanal , a sampling technique for estimating species composition and pasture yield in the field. IWM is a long-term ecological approach and after 3 years, major trends were just becoming apparent. This study shows that pasture composition can be manipulated to increase productivity and sustainability. It demonstrates that broad-leaved weeds can be reduced when high level pasture background management and chemical control are combined.