Scale and spatial structure effects on the outcome of barley cultivar mixture trials for disease control

► Barley cultivar mixtures showed a greater reduction in powdery mildew infection compared with the component monoculture mean if structured. ► There was a trend towards greater reductions in disease at the low fertiliser level and smaller plot size. ► The plot size and structuring effects may be explained by the interaction between host heterogeneity structure and pathogen dispersal scale effects. ► These findings have implications for methods of trialling mixtures for large-scale field use and for testing component combining ability.