As an element of biological disease and pest management, field trials with species mixtures of cereals were carried out from 1983–1989. Mixtures of winter-rye/winter-wheat (food grains) and spring-barley/oats (feeding grains) were tested for their ability to reduce fungal leaf damage. Significant and regular reductions in disease frequency and intensity were achieved. This was especially true forErysiphe graminisf.sp.hordeiandPuccinia reconditaf.sp.tritici, but also included leaf spot diseases caused byDrechslera avenaeandRhynchosporium secalis.Compared with fungicide applications, mixtures of two species showed adequate effects in reducing disease intensity. Harvesting of mixtures never presented a problem. This was especially due to a conspicuous maturity adjustment. Species mixtures of cereals therefore deserve more attention in environmentally safe cropping systems.