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Root rot’s impacts likened to coral bleaching



July 14, 2017

What could be worse than coral bleaching? A combination of extended warm and higher summer rainfall have created a perfect storm for the further spread of root rot, Phytophthora cinnamomi, whose impact on terrestrial ecosystems has been likened to recent coral bleaching events.

The impact of phytophthora on mainland Australia has been a growing problem in the previous two decades where its spread across every state and territory is continuing, thanks to a combination of natural dispersal as well as human activity.

Scientists are warning the public, not just gardeners, that its further spread is becoming a problem similar to and potentially bigger than coral bleaching on the Great Barrier Reef. The disease devastates vast areas of bushland and national parks across the country, changing entire ecosystems by killing large numbers of trees and shrubs at an alarming rate.

Horticultural scientist, Sabrina Hahn, has likened its effects to coral bleaching recently by saying:


Trees and shrubs are the lifeblood of terrestrial ecosystems, providing food and habitat for a myriad of fauna. When they are suddenly removed, fauna is displaced and habitat is fragmented, making it harder for remaining species to survive. The same process is unfolding on the Great Barrier Reef with bleaching, much publicised recently, but the impact of phyophthora has been gaining ground on terra firma for decades.

The challenges it poses for natural parks managers is vast, as the pathogen can be spread by attaching its spores to boots, mountain bike wheels, packs – anything that might come into contact with soil in affected areas.

Phytophthora is technically a water mould, not a fungus. It has a stage in its reproduction where its spores are ‘motile’, meaning they can move around thanks to a flagellum that allows them to motor around for short distances. This feature distinguishes them from fungi. Phytophthora is also highly pathogenic, releasing huge amounts of these spores that readily infect other healthy plants in the soil around it. It kills by attacking young root tissue, starving plants of nutrition and water, but can be present up to 2m up the trunks of trees as well.


It has been introduced to many gardens by people using materials from bushland. Chipped eucalyptus mulch from infected trees has been the main cause of its march into gardens, but that doesn’t mean your exotics are safe. It is a disease that doesn’t discriminate and will readily kill a gum tree, pine, citrus, rose or grass tree, often in matter of weeks after infecting it.

What can you do?

Gardeners and outdoor lovers alike have been asked to take precautions.

Gardeners have been urged to practice good hygiene – cleaning tools and materials thoroughly with diluted methylated spirits when moving between areas, even if the area is not infected. Not reusing any materials such as mulch, logs, rocks or mosses from sites known to be infected. Also, ask your mulch supplier where the mulch you buy comes from and do they guarantee it free phytophthora, good dealers will be able to tell you.

Hikers, mountain bike riders and campers have been urged to use foot-washing stations where they find them and to thoroughly disinfest all their gear after spending time in national parks and bushland.

Check out the ABC website for more information on combating this devastating disease.


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