Observations on the Epidemiology and Effect on Grain Yield of Brown Rust in Spring Barley

SUMMARY In observations made over four seasons, counts of brown rust spores trapped above barley crops and infections of healthy plants placed within crops, indicated that there was a high risk of infection on days when at least 5 far of dew were recorded following a day on which the maximum temperature was greater than 15°C. In spray‐timing trials, the fungicidal sprays applied between the first appearance of brown rust in the crop and the beginning of the exponential phase of the epidemic usually were associated with the highest yields. The relationships between levels of brown rust and yields in these trials is discussed in connection with their relevance to the estimation of losses caused by the disease.