A single‐shoot assessment method was used at 18 locations in England and Wales from 1976 to 1981 to compare the average yield of large numbers of shoots naturally infected with sharp eysspot (Rhizoctonia cerealis) with the yield of healthy shoots. Slight sharp eyespot infection had. on average, little effect on yield. Moderate infection significantly reduced yield per ear and 1000‐grain weight by 5 and 4 respectively. Severe infection significantly reduced yield per ear and its components, grain number per ear and 1000‐grain weight, by 26, 20 and 11 respectively. Application of the formula y = 0‐05 x1+ 0.26 x2(where y = percentage yield loss, X1= percentage of moderately Infected shoots and x2= percentage of severely infected shoots) to the results of ADAS winter wheat disease surveys from 1975 to 1982 gave estimated national yieid losses due lo sharp eyespot ranging from less than 0.1 to 0.9. Survey results indicated that increased disease incidence and associated yield losses are associated with trends towards earlier drilling and, possibly, with increased use of carbendazimgenerating fungicides, combined with more favourable infection
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