Eighteen experiments were carried out over a 6-year period (1989–94) on three different soil types to compare the effects of a broad-spectrum fungicide, applied as 1-, 2- or 3-spray programmes at different growth stages, to control foliar diseases on early and later-sown Blenheim malting barley. Powdery mildew, caused by Erysiphe graminis (Blumeria graminis) f. sp. hordei, was the dominant disease in all 6 years. Sowing date had a major effect on grain yield and ex-farm quality of the malting barley. The earlier-sown treatments gave significantly greater yield than the later-sown in 13 of the experiments, and significantly lower grain N concentrations and screenings (small grains <2·2mm) in 14 and 16 of them, respectively.

Early and more frequent fungicide applications improved grain yield and reduced grain screenings but had no significant effect on grain N. Early-applied fungicide (i.e. before GS 33) was generally the most effective in controlling disease, increasing yield and reducing screenings. The magnitude of the response depended on disease severity. In those years when disease was low on the early-sown crops (1989,1991 and 1994), the early-applied 1-spray programme and 2-spray programmes increased grain yields by relatively small amounts in both early and late-sown crops. In the other 3 years (1990,1992 and 1993), when disease severity was greater, the early-applied 1-spray programme and 2-spray programmes gave much greater grain yield increments on both early and late sowings. The 3-spray fungicide programme gave the greatest yields in most of the experiments but they were not significantly greater than the best of all the other treatments. Grain screenings were reduced by fungicide applications in both early and late-sown crops, but the early-applied 1-spray programme and 2-spray programmes were generally the most effective in reducing screenings.