Combining a weed traits database with a population dynamics model predicts shifts in weed communities

A functional approach to predicting shifts in weed floras in response to management or environmental change requires the combination of data on weed traits with analytical frameworks that capture the filtering effect of selection pressures on traits. A weed traits database (WTDB) was designed, populated and analysed, initially using data for 19 common European weeds, to begin to consolidate trait data in a single repository. The initial choice of traits was driven by the requirements of empirical models of weed population dynamics to identify correlations between traits and model parameters. These relationships were used to build a generic model, operating at the level of functional traits, to simulate the impact of increasing herbicide and fertiliser use on virtual weeds along gradients of seed weight and maximum height. The model generated ‘fitness contours’ (defined as population growth rates) within this trait space in different scenarios, onto which two sets of weed species, defined as common or declining in the UK, were mapped. The effect of increasing inputs on the weed flora was successfully simulated; 77% of common species were predicted to have stable or increasing populations under high fertiliser and herbicide use, in contrast with only 29% of the species that have declined. Future development of the WTDB will aim to increase the number of species covered, incorporate a wider range of traits and analyse intraspecific variability under contrasting management and environments

A TaqMan real-time PCR assay for Rhizoctonia cerealis and its use in wheat and soil

Rhizoctonia cerealis causes sharp eyespot in cereals and the pathogen survives as mycelia or sclerotia in soil. Real-time Polymerase Chain Reaction (qPCR) assays based on TaqMan chemistry are highly suitable for use on DNA extracted from soil. We report here the first qPCR assay for R. cerealis using TaqMan primers and a probe based on a unique Sequence Characterised Amplified Region (SCAR). The assay is highly specific and did not amplify DNA from a range of other binucleate Rhizoctonia species or isolates of anastomosis groups of Rhizoctonia solani. The high sensitivity of the assay was demonstrated in soils using a bulk DNA extraction method where 200 μg sclerotia in 50 g of soil were detected. DNA of the pathogen could also be amplified from asymptomatic wheat plants. Using the assay on soil samples from fields under different crop rotations, R. cerealis was most frequently detected in soils where wheat was grown or soil under pasture. It was detected least frequently in fields where potatoes were grown. This study demonstrates that assays derived from SCAR sequences can produce specific and sensitive qPCR assays

An ecological future for weed science to sustain crop production and the environment. A review

Sustainable strategies for managing weeds are critical to meeting agriculture's potential to feed the world's population while conserving the ecosystems and biodiversity on which we depend. The dominant paradigm of weed management in developed countries is currently founded on the two principal tools of herbicides and tillage to remove weeds. However, evidence of negative environmental impacts from both tools is growing, and herbicide resistance is increasingly prevalent. These challenges emerge from a lack of attention to how weeds interact with and are regulated by the agroecosystem as a whole. Novel technological tools proposed for weed control, such as new herbicides, gene editing, and seed destructors, do not address these systemic challenges and thus are unlikely to provide truly sustainable solutions. Combining multiple tools and techniques in an Integrated Weed Management strategy is a step forward, but many integrated strategies still remain overly reliant on too few tools. In contrast, advances in weed ecology are revealing a wealth of options to manage weedsat the agroecosystem levelthat, rather than aiming to eradicate weeds, act to regulate populations to limit their negative impacts while conserving diversity. Here, we review the current state of knowledge in weed ecology and identify how this can be translated into practical weed management. The major points are the following: (1) the diversity and type of crops, management actions and limiting resources can be manipulated to limit weed competitiveness while promoting weed diversity; (2) in contrast to technological tools, ecological approaches to weed management tend to be synergistic with other agroecosystem functions; and (3) there are many existing practices compatible with this approach that could be integrated into current systems, alongside new options to explore. Overall, this review demonstrates that integrating systems-level ecological thinking into agronomic decision-making offers the best route to achieving sustainable weed management

How to use a “virtual field” to evaluate and design integrated weed management strategies at different spatial and temporal scales

International audienc

Influence des successions culturales sur les maladies du pied et des racines du blé d'hiver

Les conséquences de différentes successions culturales sur les maladies du pied et des racines ont été étudiées sur une culture de blé d'hiver conduite de manière homogène. Les niveaux d'infestation de piétin-verse (Pseudocercosporella herpotrichoides), piétin-échaudage (Gaeumannomyces graminis var tritici) et rhizoctone (Rhizoctonia cerealis) ont été notés à la floraison sur tige et racines. Les résultats obtenus ont permis de proposer un modèle simple de l'effet du précédent et de l'antéprécédent sur les 3 maladies, basé sur le classement des risques des précédents culturaux en 3 groupes : hôte, culture amplificatrice et non-hôte pour le piétin-échaudage et le rhizoctone, hôte fort/faible, culture amplificatrice et non-hôte pour le piétin-verse. Alors que les cultures hôtes tendent à augmenter le risque et les non-hôtes à le diminuer, les cultures du groupe des amplificatrices (maïs, ray-grass...) n'entraînent un risque que si elles sont associées dans le temps à des cultures hôtes.Influence of crop succession on foot and root diseases of wheat. The consequences of different crop successions on foot and root diseases were analysed on a subsequent winter wheat crop managed identically, regardless of crop succession. At flowering, tillers and roots were assessed for eyespot (Pseudocercosporella herpotrichoides), take-all (Gaeumannomyces graminis var tritici) and sharp eyespot (Rhizoctonia cerealis). As a consequence, we can propose a simple model of the effect of the preceding crop and the 1 before that on the 3 diseases. This model is based on a crop classification into 3 groups: host, amplifying crop and non-host for take-all and sharp eyespot; and 'strong/weak' host, amplifying crop and non-host for eyespot. Whereas host crops tend to increase and non-host crops to decrease disease risk, amplifying crops (maize, ryegrass, etc) can only increase risk if they are associated with host crops

Influence des successions culturales sur les maladies du pied et des racines du ble d'hiver

National audienceThe consequences of different crop successions on foot and root diseases were analysed on a subsequent winter wheat crop managed identically, regardless of crop succession. At flowering, tillers and roots were assessed for eyespot (Pseudocercosporella herpotrichoides), take-all (Gaeumannomyces graminis var tritici) and sharp eyespot (Rhizoctonia cerealis). As a consequence, we can propose a simple model of the effect of the preceding crop and the 1 before that on the 3 diseases. This model is based on a crop classification into 3 groups: host, amplifying crop and non-host for take-all and sharp eyespot; and ’strong/weak’ host, amplifying crop and non-host for eyespot. Whereas host crops tend to increase and non-host crops to decrease disease risk, amplifying crops (maize, ryegrass, etc) can only increase risk if they are associated with host crops.Les conséquences de différentes successions culturales sur les maladies du pied et des racines ont été étudiées sur une culture de blé d’hiver conduite de manière homogène. Les niveaux d’infestation de piétin-verse (Pseudocercosporella herpotrichoides), piétin-échaudage (Gaeumannomyces graminis var tritici) et rhizoctone (Rhizoctonia cerealis) ont été notés à la floraison sur tige et racines. Les résultats obtenus ont permis de proposer un modèle simple de l’effet du précédent et de l’antéprécédent sur les 3 maladies, basé sur le classement des risques des précédents culturaux en 3 groupes : hôte, culture amplificatrice et non-hôte pour le piétin-échaudage et le rhizoctone, hôte fort/faible, culture amplificatrice et non-hôte pour le piétin-verse. Alors que les cultures hôtes tendent à augmenter le risque et les non-hôtes à le diminuer, les cultures du groupe des amplificatrices (maïs, ray-grass...) n’entraînent un risque que si elles sont associées dans le temps à des cultures hôtes

Recherche de systèmes de cultures à moindre risque de maladies du pied et des racines de blé - A : Influence de la succession culturale

International audienc

Using a sensitivity analysis of a weed dynamics model to develop sustainable cropping systems. II. Long-term effect of past crops and management techniques on weed infestation

International audienceBoth scientists and farmers are confronted by a similar question: which current and past cropping system components will influence the present weed flora, and how? This information is necessary to optimize both cropping systems for weed control, and quality and cost in surveys and monitoring schemes. The present study addressed these questions with a sensitivity analysis to input variables of a cropping system model, ALOMYSYS, that predicts weed dynamics in interaction with pedo-climatic conditions. The study ranked cropping system components according to their impact on weed infestation in winter wheat, showing for instance that though crop succession was crucial, current and past tillage strategies influenced grass weed densities even more. Crops were not only ranked as a function of the resulting weed risk but the latter was also linked to crop species traits, i.e. crop type, usual sowing period and emergence speed. A previous winter v. spring crop thus increased weed density by 72% in the following winter wheat; a late-sown v. early sown winter crop by 26%, a slow v. fast-emerging winter crop by 17%, and a lower competitive ability by 9%. Similarly, the characteristics of each crop management technique (tillage, catch crop, secondary crop, mowing, mechanical weeding, herbicides, nitrogen fertilizer, manure and harvest) were quantified. For instance, the timing of the first tillage operation was crucial prior to the analysed winter wheat crop while the choice of the tool used even 5 years previously still influenced weed infestation in the current year; a catch crop prior to previous spring sown crops reduced the current infestation regardless of catch crop sowing dates and densities, but the reductive effect could be lost if the field was tilled several times to destroy the catch crop. The advice synthesized here and in a companion paper (Colbach & Meziere 2012). will be valuable to design innovative, integrated cropping systems, indicating (1) which cropping system components to modify to produce the largest effect, (2) for how long past practices must be considered when choosing current options and (3) the optimal options for the different management techniques. Points (1) and (2) are also valuable to identify data to record in surveys, though still resulting in a total of 232 variables. In a second step, these detailed variables were therefore simplified and aggregated to determine a smaller set of 22 synthetic variables easily recorded in surveys, such as the proportion of winter and spring crops during the last 10 years (instead of the actual crop sequence), the proportion of crops sown in summer, early autumn, late autumn, early spring and late spring during the last 5 years (instead of exact sowing dates), the ploughing frequency (instead of ploughing dates and characteristics), the mean number of herbicide sprayings per year (instead of dates), etc. This reduced survey list will reduce the cost of surveys as well as increase the number and quality of surveys as more farmers will be ready to participate and there will be fewer uncertainties in the answers