Above: Dead and dying grass trees (Xanthorrhoea sp.) due to root rot in South Australia. Photo © 2014 Dept. of Environment, Water and Natural Resources, SA.
With a scientific name meaning “to destroy plants”, there’s no doubt that root rot (Phytophthora cinnamomi) is a foe of our forests. Since its introduction from Southeast Asia in the late 1800s, the pathogen has established itself across Australia, causing dieback in native plants, agricultural crops and horticultural species.
In South East Queensland (SEQ), where root rot is the most destructive disease to effect avocado crops, its management has traditionally been agriculturally focused. So earlier this year when I noticed pathogen hygiene stations installed in some Gold Coast hinterland and Scenic Rim national parks – including those listed as World Heritage Area – I wondered what had triggered the decision to manage the pathogen in the region’s natural areas, and whether the risk root rot posed to our regions’ rich biodiversity was increasing.
Phytophthora survives in water and soil, and has the potential to cause considerable damage to an area’s biodiversity by changing the species composition and structure of a forest, and therefore the habitat available to the wildlife using it. It affects a plant’s feeder roots (the dense network of roots close to the surface), which after infection, darken in appearance and can no longer absorb water and nutrients, leaving the plant exposed to disease and other pathogens. The leaves of affected plants yellow and wilt before drying out and in most cases, the plant ultimately dies. The time taken to die can range from months to years.
When I contacted the Queensland Parks and Wildlife Service (QPWS) to find out more about the relatively recent installations, a spokesperson advised the hygiene stations – which have been installed at walking track entrances in Lamington, Springbrook, Moogerah Peaks and Mount Barney National Parks – are just a precautionary measure. They explained that when federal funding became available in late 2013, QPWS took the opportunity to enhance the protection of the world-recognised area and advised that, “whilst some grass trees were recently affected in the Moogerah Peaks National Park, outbreaks are extremely rare in SEQ and no cases of dieback caused by root rot have been recorded in any of the national parks listed as World Heritage Area”.
Whilst it is good news that there have been limited root rot outbreaks in national parks to-date, the installation of hygiene stations serves as a reminder of the pathogen’s potential to spread and prosper.
Like any fungus, root rot prefers warm damp environments and under these conditions releases zoospores into the surrounding soil, which then spread through stormwater and drainage water. It is highly adaptable and in periods of cooler weather or drought will release chlamydospores and oospores, which can survive for long periods in soil or dead plant material until conditions are once again favourable, at which point it infects new plants. Its climatic preferences mean that Phytophthora tends to establish in areas that receive more than 600 mm of rainfall annually, meaning that most of SEQ is a suitable environment for the fungus.
Root rot is already well established in Tasmania, Victoria and Western Australia’s south, where management measures have been implemented in natural areas and forestry reserves to reduce the pathogen’s spread and minimise its impact. Despite efforts though, it continues to affect hundreds of species of native plants including those considered iconic to the Australian landscape, such as grass trees (Xanthorrhoea spp.) and eucalypts (Eucalyptus spp.).
The country’s most impacted regions are all popular destinations known for their natural beauty where people regularly hike, ride and drive through natural areas. As well as animals and water runoff, bushwalkers and machinery are vectors of root rot so it is important that those using our natural areas understand how the fungus is spread and ensure they don’t play a role in contaminating other areas.
A QPWS spokesperson recommends that to do your bit to limit the spread of root rot by “making sure your shoes, tyres and equipment are free of soil at the start and end of your stay, keep on designated tracks and comply with closure signs. Use hygiene stations provided and also disinfect equipment and vehicles before travelling into other parks and forests”.
Left and above: Bushwalkers should use pathogen hygiene stations, where installed, to clean their boots and help prevent the spread of root rot. Photos by Lexie Webster
Article by Lexie Webster Land for Wildlife Officer City of Gold Coast