THE AUSTRALIAN SUGARCANE ORANGE RUST EPIPHYTOTIC

摘要

RESEARCH into orange rust (caused by Puccinia kuehnii) was urgently conducted in 2000 and 2001 in order to minimise the effect of this once minor leaf disease on sugarcane yields in Australia. Losses from the disease exploded in 2000 leading to one ofthe worst epiphytotics in the history of the Australian industry. Research addressed fungicidal control in experiments located in the central Queensland region. Several chemicals with activity against rust pathogens were screened and the most effectiveand economic application schedules identified. Good fungicide control was provided by the fungicide tebuconazole ('Folicur') and extensive commercial spraying was undertaken in some 2001 crops. Fungicide and breeding trials were used to estimate yield losses caused by the disease; losses were as high as 38-40% in the years 2000 and 2001. With the down-turn in sugar prices, and the cultivation of more resistant varieties, commercial application of fungicide was limited in 2002 and 2003. Commercial cultivars and promising clones were screened for disease resistance and a high level of resistance was found both in parent canes and seedlings in the BSES selection program. Assistance was provided to industry to change from the susceptible Q124 to more resistant commercial varieties. An Orange Rust Task Force helped growers find planting material of alternative varieties, decide which new varieties to accelerate and assisted in obtaining emergency registration for a commercial fungicide application. The effect of weather conditions on disease occurrence was also investigated so that industry could be notified when weather conditions were conducive for disease development. This assisted with decisions related to fungicide application. The disease may stillbe seen but is at much lower levels. Susceptible clones are still being discarded from the breeding program, and disease levels in varieties with moderate resistance are being monitored. The orange rust epiphytotic illustrates again that sugar industriesshould never become too reliant on one variety but should have a mixture of varieties to protect against disease outbreaks. Even minor endemic diseases may develop into major disease outbreaks and threaten the existence of an entire industry.