Prediction of sorghum downy mildew risk in Australia using daily weather data

Abstract

The temporal and regional distributions of the potential number of infection events of the exotic disease sorghum downy mildew in Australia were predicted for the years 1957–1998. A set of rules based on overseas research on the influence of environmental factors on infection and sporulation was used to interrogate daily climatic data from 1957 to 1998 for 53 selected localities. Between November and February, sorghum was at arelatively low risk of infection from downy mildew, with the risk gradually increasing during the summer, reaching the greatest risk in May for most localities. During March to May there were geographical south-north, as well as west-east, increasing gradients of predicted downy mildew events in Queensland and New South Wales. In winter and early spring, the analysis indicated that disease would occur only in the coastal regions of Queensland, with serious implications for breeders’ nurseries in these areas. The temporal and regional distributions of events were closely related to those of relative humidity, night temperature and night length. Sorghum downy mildew was predicated to be a minor problem in most part of New South Wales.