The effects of uneven, patchy cultivar mixtures on disease control and yield in winter barley

Three winter barley cultivars were mixed in equal proportions but in different ways to give different patterns of spatial heterogeneity. The mixtures were sown in large field plots over three successive years and disease severity and yield were compared between the mixtures and the mean of the components grown as monocultures. Most mixtures significantly reduced disease in all years. The mixture composition, which appeared to generate a discrete pattern of small patches of the component cultivars, gave a yield advantage in 2 years, while the mixture which was pre-mixed most homogeneously gave no significant yield advantage in these trials. The cost of homogeneous mixing is therefore unlikely to be recovered in increased yields, compared with a simpler, imprecise mixing of the components in the seed hopper prior to sowing.