Modelling the population dynamics of annual ryegrass (Lolium rigidum) under various weed management systems

A mathematical model for simulating the population dynamics of annual ryegrass (Lolium rigidum) has been constructed using previous reported data. The model is used to describe the bahaviour of the population in the absence of control practices and to predict the effect of various control strategies. In the absence of control and under continuous winter barley cropping the population grew sigmodally, reaching an equilibrium at a density of 2357 seeds m(-2) (1508 seedlings m(-2)). Annual application of herbicides at 100%, 50% and 25% the standard rate resulted in reductions in the equilibrium position of the population of 90%, 80% and 70%, respectively. Using various types of cultural control tactics (delayed seeding, crop competition, seed catching, crop rotation) resulted in partial control of this weed, maintaining relatively high population levels. Keeping the prevailing crop rotation (continuous barley) and integrating the use of various chemical and cultural tactics resulted in the best long-term results with a seed bank equilibrium level of 77 seeds m(-2) (49 seedlings m(-2)). Results from the sensitivity analysis indicate that the size of ryegrass populations is particularly vulnerable to small changes in the reproductive capacity and the loss of seeds. These two processes should be studied with greater detail in order to provide possible clues for the control of this weed. Furthermore, control tactics specifically focused on those life cycle periods should be investigated. (C) 2004 Elsevier Ltd. All rights reserved.