The Diversity model: a multi-species, multi-herbicide tool for strategy development in Australian cotton cropping

Abstract

Because herbicide resistance evolves in very large populations over periods of several (or many) years, modelling has been an important tool for investigating the dynamics of the problem. More recent models can also simulate spatial evolutionary and management dynamics. In some cases, models have been used to develop on-ground strategies for dealing with developing, nascent, or dominating resistant populations. The Diversity model builds on existing modelling efforts but goes a step further: it tracks the evolution of resistance to three herbicides in four weed species in the same environment. The Diversity model has been designed to test strategies for use in new cropping cotton varieties with multiple herbicide tolerances, in an Australian context. The Diversity model is constructed in Python 3, extending the existing mono-gene resistance model SHeRA. It tracks resistance as single-gene and polygene traits, and as target-site, non-target-site, and gene amplification mechanisms, and includes both the three target herbicides and a complete range of other weed management options for use in prospective strategies. We understand now that diversity is the answer to herbicide resistance. Stacked herbicide tolerance in new crop varieties offers greater potential for herbicide diversity, but the results of their use in vivo will take time to emerge. With the Diversity model, we aim to quantify just how diverse ‘diversity’ actually is, and to develop and release strategies of practical use in time to defend the herbicide susceptibility that remains.