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

The temporal and regional distributions of the potential number of infectio n events of the exotic disease sorghum downy mildew in Australia were predi cted for the years 1957-1998. A set of rules based on overseas research on the influence of environmental factors on infection and sporulation was use d to interrogate daily climatic data from 1957 to 1998 for 53 selected loca lities. Between November and February, sorghum was at a relatively low risk of infection from downy mildew with the risk gradually increasing during t he summer, reaching the greatest risk in May for most localities. During Ma rch to May there were geographical south-north, as well as west-east, incre asing gradients of predicted downy mildew events in Queensland and New Sout h Wales. In winter and early spring, the analysis indicated that disease wo uld occur only in the coastal regions of Queensland, with serious implicati ons for breeders' nurseries in these areas. The temporal and regional distr ibutions of events were closely related to those of relative humidity, nigh t temperature: and night length. Sorghum downy mildew was predicated to be a minor problem in most part of New South Wales.