Influence of Spray Timmg for the Control of Powdery Mildew on the Yield of Spring Barley

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Abstract
SUMMARY: The highest mean yield increase from a single spray of tridemorph applied for the control of powdery mildew was 540 kg/ha (12·1 per cent) more than the yield of unsprayed crops. Two or more sprays increased yields by 703 kg/ha (15·6 per cent). The more susceptible cultivars gave highest yield increases. Crops near winter barley gave higher yield increases than crops not near winter barley and responded best to early sprays whereas the other crops responded best to sprays applied later. Highest yield increases were obtained when sprays were applied as soon as 3–5 per cent of the leaf area of the oldest leaves was affected by mildew and this was the best criterion for timing sprays. Usually such sprays were applied during the growth stages 6–9 so that applying the fungicide with the herbicide up to growth stage 5 would not give the highest yield increase.The best relationship between mildew and yield increase was obtained when a cumulative mildew index (per cent mildew x days) was used.