Simulating weed persistence and herbicide resistance in the northern grain region using a validated crop growth model with extensions for seedbank dynamics and mating.

The dynamics of weeds in northern grain cropping systems are complex, due to the relatively variable potential growing conditions in any given year. Weeds may germinate and grow during a fallow season or may be forced to compete with a crop. Rainfall is unpredictable. Due to this high variability in cropping and rainfall conditions, soil moisture, nutrition, and covering organic matter all vary widely from one year to the next; similarly, interspecific competition and seed bank dynamics are equally likely to vary. Accordingly, any attempt to model the population dynamics of northern region weeds appears to require a relatively complex approach. We have coupled a well-verified crop growth model (APSIM) with seed bank and mating sub-models (implemented in Vensim) in an attempt to deal with this level of environmental variability, and to test the effects of various aspects of the cropping system on the rate at which resistance to glyphosate might evolve in local weed populations. APSIM deals with the dynamics of the weeds and crops during the growth phase. The Vensim extensions deal with the effects of mating parameters (that is, the effect of the level of self-compatibility in the weed species) and seed bank dynamics, such as the level of mortality in the seed bank, and the germination rate in a particular season.