SPATIAL-ANALYSIS OF WHEAT STRIPE RUST EPIDEMICS

The distribution of wheat stripe rust infection was analysed using fit to frequency models, dispersion indices and the regression of mean crowding on mean density. Disease was measured as severity using a sample unit of ten consecutive tillers along a drill row, with a W sample pattern in the field and the regression relationship percentage severity = -0.01 + 0.02 (percentage incidence). As the epidemic progressed, the spatial pattern of disease changed from random to aggregated, to random or uniform, for high severity values. Infections on the top three green fully expanded leaves gave consistent results by different methods and in different crops and seasons.