Summary Conyza bonariensis is a South American native annual Asteraceae that has been introduced to the Mediterranean, where it behaves as a ruderal plant and a weed that is difficult to control in several crops. The development of predictive models can contribute to control measures at early growth stages, but currently there are no studies to predict seedling emergence of Conyza species. Our objectives were to develop and evaluate a model for predicting emergence response of C. bonariensis to the soil hydrothermal environment. A hydrothermal seed germination model was fitted to time course germination data from germination tests carried out at different constant temperatures and water potentials with the aim of establishing the hydrothermal parameters characterising C. bonariensis seed germination. The relationship between cumulative seedling emergence and cumulative hydrothermal time under field conditions was analysed using the Gompertz function. Model development was based on 2 years' data from a field experiment. Base temperature and base water potential for seed germination were estimated at 10.6°C and −0.70 ± 0.151 MPa, respectively. The emergence model showed a very good fit to the experimental data. According to this model, seedling emergence starts at 15 accumulated hydrothermal time (HTT) after sowing, and 50 and 95% emergence is completed at 53 HTT and 105 HTT, respectively. For model evaluation, independent field experiments were carried out in two localities. Cumulative seedling emergence was accurately predicted by the model. Results indicate that this model can be useful as a predictive tool contributing to effective control of C. bonariensis populations.

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Phalaris brachystachys is a common and troublesome weed in winter cereals in Mediterranean countries. A deterministic model was developed to simulate P. brachystachys seedbank dynamics in the wheat-sunflower rotation, a commonly practiced cropping system in southern Spain, under different herbicide-based management scenarios: no herbicide application, full herbicide dose (standard rate) and two reduced dose rates (75 and 50% of the standard rate). Without treatment, a steady increase of the seed bank is predicted up to an equilibrium level of 54,859 seeds m -2 (575 plants m -2 ) after 25 years. Full dose herbicide applications in wheat years resulted in a progressive seed bank decline over years. Reducing the efficacy of the herbicide by using 50% or 75% of the recommended rate resulted in no long-term seed bank decline. Instead, a population increase until equilibrium densities is predicted. A sensitivity analysis showed that seedling survival and fecundity were the most sensitive demographic parameters under the full dose strategy, whereas fecundity and seedbank mortality were the most sensitive parameters under reduced dose strategies. Reduced dose strategies tended to be less sensitive than the full dose strategy. Simulations indicated that longterm control of this weed may be attained under full dose, highly effective, herbicide applications. Unless effectiveness could be maintained at very high levels, reduced herbicide doses may not be a recommendable option for the long-term control of this species in a wheat-sunflower rotation.Additional key words: population model; seed bank; sensitivity analysis; short-spiked canarygrass; simulation; sunflower-wheat rotation. Resumen Estrategias para el control con herbicidas de Phalaris brachystachys en una rotación trigo-girasol: un modelo de simulaciónPhalaris brachystachys es una de las malas hierbas más importantes en el cultivo de trigo en los países mediterráneos. Un modelo determinístico fue desarrollado para simular la dinámica del banco de semillas de P. brachystachys en una rotación trigo-girasol, un sistema de cultivo utilizado frecuentemente en el sur de España, bajo diferentes escenarios de manejo basado en el uso de herbicidas: sin herbicidas, dosis completa (recomendada por el fabricante), y dos dosis reducidas (75% y 50% de la dosis recomendada). Al usar el tratamiento sin herbicidas, el banco de semillas alcanza un nivel de equilibrio con 54.859 semillas m -2 (575 plantas m -2 ) a los 25 años. La aplicación de la dosis completa en el año de trigo resultó en una reducción progresiva del banco de semillas. El uso de dosis reducidas no resultó en una disminución en el banco de semillas a largo plazo. El análisis de sensibilidad mostró que la supervivencia de plantas y la fecundidad son los parámetros demográficos más sensibles al aplicar la dosis completa del herbicida, mientras que la fecundidad y la mortalidad en el banco de semillas fueron los parámetros más sensibles al aplicar las dosis reducidas de herbicidas. De acuerdo con el análisis de...

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