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 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 popula-tions 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. Additional key words: density-dependence, population model, seed bank, sensitivity analysis, short-spiked canary-grass, simulation, winter wheat