New strain of Mrytle rust hits Australia

Friday 8 Dec 2017

The angle-stemmed myrtle had been looking like a species saved just in time from extinction. Several hundred trees had been bred from a mere 75 survivors lingering in tattered scraps of rainforest around Logan City, just south of Brisbane. Then in 2010 a feared disease slipped past Australia’s quarantine. The new leaves that form on myrtles today are apt to sprout yellow pustules, turn black and fall off. Myrtle numbers are falling.

The disease – myrtle rust – has shown what it can do in South America, its native home. Brazil has the world’s largest plantations of Australian eucalypts – more than six million hectares tended by four million workers – and problems struck in the 1970s when seedlings began dying en masse. The survivors grew into trees too deformed to harvest. Losses of up to 40 per cent in wood production were reported. The industry survived the crisis by investing heavily in breeding eucalypt varieties that resist the disease. Some of these varieties are now at risk from a newly discovered strain of myrtle rust.

Australia could lose 14.8 per cent of its eucalypt timber output from this disease. That is a worst-case scenario produced in 2006 for the Primary Industries Ministerial Council, when the rust turned up in Hawaii and began killing trees there.

Australia, the land of myrtles, has much to lose. Eucalypts are members of the myrtle family (Myrtaceae), Australia’s largest plant family, along with tea-trees, bottlebrushes, paperbarks, lilly pillies and others – some 2250 species altogether. Myrtle rust has been reported infecting more than 240 species, with some rainforest trees dying so quickly that scientists have voiced fears they may “become extinct in the wild within the next decade”.

The rust spread dramatically inside Australia after it was found in a large nursery near Gosford, infecting hundreds of plants. How it reached Australia is not known, though the nursery trade helped it spread rapidly along the eastern seaboard, reaching Tasmania and the northern tip of Queensland by 2015. Its spores also blow on the wind and travel on honeybees.

Because the strain of myrtle rust that has reached Australia is not one that blights eucalypts, one view is that the risk to Australia has been overstated. But John McDonald, biosecurity manager of the Nursery and Garden Industry of Australia, rejects any talking down of the disease as “just absolute head-in-the-sand stuff”. More >>.


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