Almost 90% of Australian blueberries are produced in northern New South Wales and Queensland. While the subtropical climate, extended growing season and evergreen cropping practices favour high blueberry yields, these conditions are also conducive to the development of fungal foliar diseases.
Blueberry rust, caused by Thekopsora minima, was first recorded in Australia in 2001 and has since spread throughout blueberry production areas in NSW and Queensland, with incursions recently reported in Tasmania and Victoria. Severe disease may result in defoliation, premature fruit drop and a late ripening crop. Severely infected plants are less productive in the following season. When disease pressure is high, lesions on fruit can affect marketability. Despite its high incidence and severity, little is known about the biology and epidemiology of T. minima in Australia.
We have shown that the blueberry rust fungus survives primarily in infected leaves retained on the plant, often asymptomatically.. In NSW, air sampling has shown that urediniospores are present at any time of the year and are the main source of new infections. Spore viability in leaf litter declines significantly after six weeks.
Blueberry producers in NSW and Queensland currently adhere to strict guidelines regarding fungicide application based on calendar sprays, and inspection of fruit prior to shipment contributing to higher production costs. Identification of factors that favour spore release and infection can assist in targeting fungicide sprays to promote more effective control, and reduce costs for growers. Factors conducive to spore production and host plant infection identified can be used to modify spray programs to target the pathogen, reducing costs and the risk of fungicide insensitivity, and improving disease control.