Integrated crop-disease models: New frontiers in systems thinking

Impacts of pest and diseases on crop productivity comprise one of the greatest existential threats to food security in the 21^st century. Despite this, crop models have historically adopted an abiotic lens. Here, we reviewed previous methods aimed at modelling effects of pests on crops and revealed a dearth of integrated approaches that account for pest lifecycles. The few integrated models that do exist tend to be empirical constructs that discount yield, with models of underpinning pest dynamics being extremely rare. Interaction between pests and crops has tended towards pest-induced reductions in plant biomass, leaf area, light interception and/or photosynthetic rates of infected plants, rather than biological modelling of the pest lifecycle per se. The use of process-based models that couple the pest-host interactions and capture the resource competition between the two are more suited to understanding the complexity of the farming system. Given that management interventions – such as crop rotation, intercropping, sowing time, nitrogen fertilisation, planting density and insecticide or fungicide use – underpin host colonisation success, we solicit advances in the modelling of management decisions to mitigate and manage pest and disease populations. Such information will become ever more crucial as global temperatures and extreme weather events increase in frequency and disease infestation proliferates. Harnessing this integrated weather-pest-crop-management continuum within farming systems models will improve farm management decisions. We conceptualise a framework using the lifecycle of blackleg disease (Leptosphaeria maculans) as an example; however, our approach could be generically adapted to other crop-pest interactions.