Mixing feed barley cultivars did not decrease leaf disease or increase grain yield

Yield reductions of up to 45% have been recorded in Western Australia when leaf disease has not been controlled using fungicides in two-row spring barley (Hordeum vulgare L.). Several overseas studies have shown that mixtures of barley cultivars can reduce the reliance on fungicides, decrease disease incidence and increase grain yield relative to pure stands. Four barley cultivars (cvv. Barque, Dash, Keel and Molloy) were mixed in 2-way, 3-way and 4-way mixtures and grown at eight sites along the 450-mm rainfall isohyet. At each site the performance of the 11 possible mixtures was compared against the same cultivars when grown as pure stands (1-way) for disease severity, grain yield and grain quality. The sites were subject to natural disease infection, with one or two leaf diseases becoming established at each site. The diseases present were: net form net blotch (caused by Pyrenophora teres f. teres) or spot form net blotch (Pyrenophora teres f. maculata) and/or powdery mildew (Erysiphe graminis f. sp. hordei). Three disease susceptible controls (cvv. Baudin, Doolup and Vlamingh) were sown at each site to rate the disease risk. At sites with a low (<5% leaf area diseased, average of three control cultivars) and moderate (5-20%) disease severity, there was no reduction in disease severity by mixing cultivars. Only with high disease severity (>20%) was there a reduction in disease severity due to mixing cultivars. No evidence was found to support the general view that mixtures themselves, or an increased number of components in the mixture, increase grain yield and grain yield stability. There were, however, cultivar combinations that improved crop performance at a site relative to one of the pure stand components, but not both. This mixture effect at a site was both cultivar and pathogen dependent. Impacts of mixtures on grain quality were variable depending on quality parameter, site and pathogen present, but were generally small.