Effects of sorghum ergot on grain sorghum production: a preliminary climatic analysis

Until 1996 the disease 'sorghum ergot' (Claviceps africana and Claviceps sorghi) was unknown in Australia. Following an outbreak near Gatton, the disease was found throughout most of the sorghum-producing areas in Queensland within 4 weeks. A climatic risk analysis was conducted to assess the likely timing and frequencies of further outbreaks of the disease across the main sorghum-producing regions of Australia. Based on the information available, likely conditions that could lead to a disease outbreak were formulated and a computer program developed to interrogate an existing database of long-term, daily weather records. Case studies were conducted for 10 key sorghum-producing locations, ranging from Narromine in central New South Wales to Mareeba in far North Queensland and Kununurra in Western Australia. For grain sorghum production, crops ∞owering in January and February are unlikely to be afiected, regardless of location. However, in up to 30% of years, late-sown grain sorghum crops and crops ∞owering before January could be afiected, depending on climatic conditions prior to and around anthesis. The frequency and timing of these events difiered strongly temporally and spatially and appeared highest in high rainfall years and in regions with relatively cooler temperatures and more frequent autumn rains. Hybrid seed production (i.e. breeding programs) and forage sorghum production are likely to be more afiected due to their inherently low pollen generation, again with strong regional variation. Further applications of the methodology, such as the development of an early warning system, based on phases of the Southern Oscillation Index, are discussed. Additional keywords: climatic risk, model, Southern Oscillation Index (SOI).