Modelling of chemical control of "Conyza" and the risk of glyphosate resistance

Se ha desarrollado un modelo de genética de poblaciones para estudiar el efecto de diferentes estrategias de manejo químicas en el control de poblaciones de Conyza y el desarrollo de resistencia a glifosato en poblaciones inicialmente susceptibles. Las estrategias de manejo se basaron en la aplicación de dos herbicidas en diferentes fechas, aislados o en mezcla, donde uno de ellos era glifosato. Las simulaciones mostraron que la aplicación de glifosato con herbicidas postemergentes controlaron más eficazmente las poblaciones de “Conyza” que las aplicaciones de glifosato con herbicidas preemergentes. Las aplicaciones tardías (principalmente en marzo) del herbicida postemergente consiguieron los mejores controles de las poblaciones y un riesgo bajo de desarrollar resistencia en poblaciones de Conyza inicialmente susceptibles.We developed a model of population genetics to study the effect of different chemical management strategies on the control of “Conyza” populations and the resistance evolution to glyphosate in initially susceptible populations. The management strategies were based on herbicides; glyphosate and another post- or pre-emergent herbicide applied alone or in mixtures at different timing. The simulations showed that glyphosate and post-emergent herbicides controlled better “Conyza” populations than glyphosate and pre-emergent herbicides. Later post-emergent herbicide applications (in March principally) reached the best control of “Conyza” populations and a low resistance risk in initially susceptible populations

Spatio-temporal dynamics of maize yield water constraints under climate change in Spain

Many studies have analyzed the impact of climate change on crop productivity, but comparing the performance of water management systems has rarely been explored. Because water supply and crop demand in agro-systems may be affected by global climate change in shaping the spatial patterns of agricultural production, we should evaluate how and where irrigation practices are effective in mitigating climate change effects. Here we have constructed simple, general models, based on biological mechanisms and a theoretical framework, which could be useful in explaining and predicting crop productivity dynamics. We have studied maize in irrigated and rain-fed systems at a provincial scale, from 1996 to 2009 in Spain, one of the most prominent >hot-spots> in future climate change projections. Our new approach allowed us to: (1) evaluate new structural properties such as the stability of crop yield dynamics, (2) detect nonlinear responses to climate change (thresholds and discontinuities), challenging the usual linear way of thinking, and (3) examine spatial patterns of yield losses due to water constraints and identify clusters of provinces that have been negatively affected by warming. We have reduced the uncertainty associated with climate change impacts on maize productivity by improving the understanding of the relative contributions of individual factors and providing a better spatial comprehension of the key processes. We have identified water stress and water management systems as being key causes of the yield gap, and detected vulnerable regions where efforts in research and policy should be prioritized in order to increase maize productivity.R. Ferrero gratefully acknowledges receipt of a grant from the Fundación Carolina. J. L. Gonzalez-Andujar and R. Ferrero were supported by FEDER (Fondo Europeo de Desarrollo Regional) and the Spanish Ministry of Economy and Competitiveness funds (AGL2012-33736). R. Ferrero and M. Lima acknowledge financial support from Fondo Basal-CONICYT grant FB-0002. We are grateful to LINCGlobal (Laboratorio Internacional en Cambio Global) for their support.Peer Reviewe

Short communication. Modelling of the population dynamics of Phalaris brachystachys Link under various herbicide control scenarios in a Mediterranean climate

The weed Phalaris brachystachys Link (short-spiked canarygrass) severely affects cereal production in regions with a Mediterranean climate. A mathematical model for simulating the population dynamics of this weed was constructed using previously reported brachystachys populations

Infestation maps and spatial stability of main weed species in maize culture

A study on the spatial distribution of the major weeds in maize was carried out in 2007 and 2008 in a field located in Golegã (Ribatejo region, Portugal). The geo-referenced sampling focused on 150 points of a 10 x 10 m mesh covering an area of 1.5 ha, before herbicide application and before harvest. In the first year, 40 species (21 botanical families) were identified at seedling stage and only 22 during the last observation. The difference in species richness can be attributed to maize monoculture favouring reduction in species number. Three of the most representative species were selected for the spatial distribution analysis: Solanum nigrum, Chenopodium album and Echinochloa crus-galli. The three species showed an aggregated spatial pattern and spatial stability over both years, although the herbicide effect is evident in the distribution of some of them in the space. These results could be taken into account when planning site-specific treatments in maize.Peer Reviewe

A predictive model for the time course of seedling emergence of Phalaris brachystachys (short-spiked canary grass) in wheat fields

Aim of study: A predictive model of the seedling emergence pattern of Phalaris brachystachys Link (short-spiked canary grass) was developed, aimed to contribute to support a more efficient management of this troublesome, competitive weed in winter cereal crops around its native Mediterranean range and in different areas of the world where it is introduced. Area of study: Southern (Andalusia) and northern Spain (Navarra). Material and methods: A model describing the emergence pattern of P. brachystachys in cereal fields based on accumulation of hydro thermal time in soil was developed and validated. For model development, cumulative emergence data were obtained in an experimental field, while an independent validation of the model was conducted with data collected in two commercial wheat fields from climatically contrasting regions of Spain. Main results: The relationship between cumulative emergence and cumulative hydrothermal time (CHT) was well described by a Logistic model. According to model predictions, 50% and 95% seedling emergence takes place at 108 and 160 CHT above base water potential for seed germination, respectively. The model accurately predicted the seedling emergence time course of P. brachystachys in the two commercial wheat fields (R2 = 0.92). Research highlights: This model is a new tool that may be useful to improve the timing of control measures to maximize efficiency in reducing P. brachystachys infestations in cereal crops

Using air thermal time to predict the time course of seedling emergence of Avena sterilis subsp. sterilis (sterile oat) under Mediterranean climate

Avena sterilis subsp. sterilis (sterile oat) is a troublesome grass weed of winter cereals both in its native range encompassing the Mediterranean up to South Asia, and in regions of America, Northern Europe and Australia where it is introduced. A better understanding of seedling emergence patterns of this weed in cereal fields can help control at early growth stages benefiting efficacy under a changing climate. With this aim, the objective of this research was to develop and validate a field emergence model for this weed based on cumulative air thermal time (CTT, ℃ day). Experiments for model setting and evaluation were carried out in experimental and commercial fields in southern Spain. Two alternative models, Gompertz and Weibull, were compared for their ability to represent emergence time course. The Weibull model provided the best fit to the data. Evaluation through independent experiments showed good model performance in predicting seedling emergence. According to the developed model, the onset of emergence takes place at 130 CTT, and 50% and 90% emergence is achieved at 448 and 632 CTT, respectively. Results indicate that this model could be useful for growers as a tool for decision-making in A. sterilis control

Weed Diversity Affects Soybean and Maize Yield in a Long Term Experiment in Michigan, USA

Managing production environments in ways that promote weed community diversity may enhance both crop production and the development of a more sustainable agriculture. This study analyzed data of productivity of maize (corn) and soybean in plots in the Main Cropping System Experiment (MCSE) at the W. K. Kellogg Biological Station Long-Term Ecological Research (KBS-LTER) in Michigan, USA, from 1996 to 2011. We used models derived from population ecology to explore how weed diversity, temperature, and precipitation interact with crop yields. Using three types of models that considered internal and external (climate and weeds) factors, with additive or non-linear variants, we found that changes in weed diversity were associated with changes in rates of crop yield increase over time for both maize and soybeans. The intrinsic capacity for soybean yield increase in response to the environment was greater under more diverse weed communities. Soybean production risks were greatest in the least weed diverse systems, in which each weed species lost was associated with progressively greater crop yield losses. Managing for weed community diversity, while suppressing dominant, highly competitive weeds, may be a helpful strategy for supporting long term increases in soybean productivity. In maize, there was a negative and non-additive response of yields to the interaction between weed diversity and minimum air temperatures. When cold temperatures constrained potential maize productivity through limited resources, negative interactions with weed diversity became more pronounced. We suggest that: (1) maize was less competitive in cold years allowing higher weed diversity and the dominance of some weed species; or (2) that cold years resulted in increased weed richness and prevalence of competitive weeds, thus reducing crop yields. Therefore, we propose to control dominant weed species especially in the years of low yield and extreme minimum temperatures to improve maize yields. Results of our study indicate that through the proactive management of weed diversity, it may be possible to promote both high productivity of crops and environmental sustainability.RF gratefully acknowledges receipt of a grant from the Fundación Carolina. JG and RF were supported by FEDER (European Regional Development Funds) and the Spanish Ministry of Economy and Competitiveness funds (AGL2012-33736 and AGL2015-64130-R). RF and ML acknowledge financial support from Center of Applied Ecology & Sustainability (CAPES; CONICYT FB 0002-2014).Peer Reviewe

Season-long seed dispersal patterns of the invasive weed Erigeron bonariensis in south-western Spain

Within-field demography of weeds exhibiting wind-mediated long distance seed movement can be largely governed by extra-field seed-source populations. Thus, for these species, a clear understanding of the temporal and spatial patterns of seed dispersal can benefit the development of effective management options. The spatial distribution of the seeds released from the onset of fruiting, in early summer, to the onset of the rainy season, in early autumn, was studied during 2 years at a Mediterranean-climate locality in Erigeron bonariensis L. (Hairy fleabane), a wind-dispersed invasive weed inhabiting ruderal environments and crop fields. Each year, a small source population was established in an open field in SW Spain and seed traps were arranged in the eight cardinal directions at distances up to 100 m (year 1), or in the NE and NW directions at distances up to 65 m (year 2). Counts of trapped seeds were carried out at 4–6 day intervals and the number of seeds released by the source population was estimated each year in most census dates. Four empirical dispersal models based on either thin-tailed or fat-tailed density kernels were tested using year 1 data for their ability to represent the spatial distribution of seeds. To test for anisotropic dispersal, model parameters were allowed to vary according to the wind pattern in each cardinal direction. Based on information criteria, a model including a fat-tailed, Log-hyperbolic secant kernel showing parameter response to the wind pattern, highlighting striking anisotropic dispersal, was selected and evaluated using year 2 data. Distance percentiles 50 and 80 attained by the seed crop released in year 1 season were modeled at 530 m and 10,498 m, respectively. The opposite quadrants encompassing the dominant downwind (N-NE) and upwind directions (S-SW) received 52.5% and 10.8% of seeds. The year 1 population, consisting of 85 plants, generated a modeled seed rain of at least 10 seeds m 2 up to 200 m downwind. Implications of results for management of this herbicide resistance-prone species are discussed.We are grateful to Carlos Carretero, Jos´e P´erez, C´ andido Ortega and Ana Lebovich for assistance with fieldwork. DC received a grant from the Spanish Society of Weed Science (SEMh). This work was supported in part by research project C03-017 (PAI-Junta de Andalucía Regional Government, Andalusia, Spain). Funding for open access provided by Universidad de Huelva / CBU

Modelización de la dinámica de poblaciones de Phalaris brachystachys bajo diversos escenarios de control herbicida en un clima mediterráneo

The weed Phalaris brachystachys Link (short-spiked canarygrass) severely affects cereal production in regions with a Mediterranean climate. A mathematical model for simulating the population dynamics of this weed was constructed using previously reported data and new information. The model was used to describe the long-term dynamics of the population in the absence of control practices and to predict the effect of various control strategies based on the annual application of herbicides at 50%, 75% and 100% of the standard rate in winter wheat. Without control the seed bank population would reach an equilibrium level at a density of 21,244 seeds m-2 after six years. Annual application of herbicides at 50%, 75% and 100% of the standard rate resulted in reductions in the equilibrium position of the population of only 5.44%, 12.27% and 26.14%, respectively. Sensitivity analysis indicated that seedbank dynamics was particularly sensitive to fecundity, seed bank mortality and seed losses, and that new control strategies should target these population parameters. The current model has highlighted the fact that herbicide tactics are not able to stabilize or decrease short-spiked canarygrass populations in winter wheat in the longer-term. Integration of herbicide applications and agronomic practices may be required to attain effective reductions of P. brachystachys populations.Phalaris brachystachys Link (alpiste) es una mala hierba que afecta de forma importante a la producción de cereales en regiones de clima mediterráneo. En este trabajo se desarrolló un modelo matemático para simular la dinámica de poblaciones de esta especie. El modelo fue utilizado para describir el comportamiento a largo plazo de las poblaciones en ausencia de prácticas de control y para predecir el efecto de varias estrategias de control basadas en la aplicación de herbicidas al 50%, 75% y 100% de la dosis recomendada en trigo de invierno. En ausencia de control el banco de semilla alcanzó un nivel de equilibrio a una densidad de 21.244 semillas m-2 al sexto año. Bajo aplicación anual de herbicidas al 50%, 75% y 100% de la dosis comercial, la posición de equilibrio de la población se redujo en sólo 5,44%, 12,27% y 23,14% respectivamente. El análisis de sensibilidad indicó que el modelo fue particularmente sensible a la fecundidad, mortalidad del banco de semilla y pérdida de semillas, por tanto, las nuevas estrategias de control deberían estar dirigidas en esta dirección. El modelo desarrollado muestra la dificultad de estabilizar o disminuir la población de alpiste a largo plazo en trigo de invierno. Con el objetivo de obtener un reducción efectiva de las poblaciones de P. brachystachys se requiere una integración de control por herbicidas con practicas culturales

Predicting global geographical distribution of "Lolium rigidum" under climate change

“Lolium rigidum Gaud.” (vallico) es una de las malezas más extendidas y perjudiciales en los cultivos de cereales de invierno. Un modelo bioclimático para esta especie fue desarrollado utilizando CLIMEX. El modelo fue validado con los registros de esta especie en Estados Unidos y Oceanía y utilizado para predecir la distribución potencial global de “L. rigidum” bajo el clima actual y dos escenarios de cambio climático. Las proyección en virtud de las condiciones climáticas actuales indican que “L. rigidum” no ocupa todo el área disponible para su expansión. Considerando los escenarios climáticos futuros, el área potencial de expansión aumentará 3,79% y 5,06% bajo los escenarios moderado y extremo, respectivamente. La proyección del modelo mostró un avance gradual de “L. rigidum” en Norteamérica, Europa, Sudamérica y Asia, mientras que en África y Oceanía se prevé una regresión. Estos resultados proporcionan Los conocimientos necesarios para identificar y poner de relieve las posibles zonas de riesgo de invasión.“Lolium rigidum” Gaud. (rigid ryegrass) is one of the most extended and harmful weeds in winter cereal crops. A bioclimatic model for this species was developed using CLIMEX. The model was validated with records from North America and Oceania and used to assess the global potential distribution of “L. rigidum” under the current climate and under two climate change scenarios. The projection under current climate conditions indicated that “L. rigidum” does not occupy the full extent of the climatically suitable area available to it. Under future climate scenarios, the infested potential area will increase 3.79% in the low-emission CO2 scenario and 5.06% under the most extreme scenario. The model projection showed a gradual advance of rigid ryegrass in North America, Europe, South America and Asia, whilst in Africa and Oceania it indicated regression. These results provide the necessary knowledge for identifying and highlighting the potential invasion risk areas