Management of Alternaria leaf and fruit spot in apples (AP02011)

This is a final research report from Hort Innovation’s historical archives. Please note that as these reports may date back as far as the 1990s, the content and recommendations within them may be superseded by more recent research.

What was it all about?

Fungicide trials in New South Wales and Queensland were revealed that different Alternaria species were responsible for Alternaria-like leaf and fruit symptoms in each state. This had resulted in slightly different fungicide spray programs being most effective in each state.
We found that more than one species of Alternaria could cause symptoms on apple leaves and fruit in Australian orchards.

Further, Alternaria was a common, widespread fungus in Australian apple orchards, with species similar to those causing production losses in Queensland and New South Wales detected in all major production areas in Australia.

It was important to distinguish between detecting Alternaria fungi in an orchard and needing to apply chemicals to manage it. Just because Alternaria was present in an orchard did not mean it was causing enough disease to warrant management. Growers were to be alert, but not alarmed.

Alternaria species were isolated from leaf lesions in almost every variety tested in a survey of the Applethorpe Apple Germplasm Repository (apple variety collection held by the Queensland Department of Primary Industries and Fisheries). However, few varieties suffered production limiting levels of disease.

In a survey of Australian apple orchards conducted in April/May 2005, we only recorded production limiting disease levels in orchards in New South Wales (Bilpin, Picton and Orange) and Queensland (Granite Belt). Varieties commonly affected in New South Wales were currently restricted to Gala, Red Delicious, Pink Lady and Fuji in descending order of importance; while in Queensland significant losses mainly occur in Gala, Pink Lady and then Red Delicious.

Our trials were led to emergency use permits for late season use of Polyram® and Delan® in 2006 – minor use permits were being sought at the time, to continue this usage, for affected areas of New South Wales and Queensland.