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In crops of winter barley, cvs Igri and Halcyon, crop structure and intensity of foliar diseases were altered by delaying the main top dressing of nitrogen until mid‐April. A single application of fungicide then was sufficient to decrease substantially the severity of fungal disease and improve grain yield at harvest. Disease control and yield responses were greatest when fungicides were applied during a 3‐week period after the main nitrogen application in April. No additional yield benefits were obtained by making two fungicide applications at growth stage (GS) 31 and GS 39.

SUMMARYLeaf size and foliar disease in winter barley increased with increasing total amounts of nitrogen applied to the crop: flag leaf areas increased at an average of 10% per 35 kg N ha‐1 Nitrogen top dressing applied in mid‐March (G.S. 31) resulted in larger leaves, more foliar disease, more straw, delayed ear emergence, fewer grains ear‐1 and less grain yield than nitrogen applied in mid‐April (G.S. 31). Application of chlormequat at G.S. 30 gave a variable response, but overall it increased fertile stems m‐2 and crop yield and decreased crop height but had no significant effect on straw yield. Fungicide treatments suppressed foliar disease and improved yield. Yield responses were greater when plant growth regulator and mid‐March nitrogen had been applied at sites where more disease prevailed than with April‐applied nitrogen. In one of the field experiments, on cv. Sonja, delaying the main nitrogen application until April, without fungicide treatment, gave a similar yield to that provided by nitrogen in March with two or three fungicide sprays.

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