Gum Tree Ebola epidemic
Red flowering gum affected by Gum Tree ebola in Canning Vale
By Neville Passmore
Western Australia’s dominant eucalyptus, the Redgum or Marri (Corymbia calophylla), is falling prey to a recently identified fungal disease. Major outbreaks have been sighted in the Margaret River and Augusta region where some of the major roads are showing infection rates of 80% of roadside Marrri trees, posing a serious danger to motorists. There are also plenty of examples in the Metropolitan area not just affecting Marri, but also the ornamental and closely related Scarlet Flowering gum (Corymbia ficifolia).
Professor Giles Hardy and Dr George Matusick from the Centre of Excellence for Climate Change Woodland and Forest Health have been studying the disease in the South West of the state. They have recently produced a free App called the "Marri App" to assist identification and encourage reporting of affected trees so a map can be made showing hot spots and to track the spread.
Ebola results in internal haemorrhaging leading to death in most instances. Gum tree Ebola is a disease of the bark and causes exudation of eucalyptus kino or red gum. The bark dies and lifts off and this results in girdling, or ringbarking of the branch or trunk of the tree. There is no cure known for either human or gum tree Ebola.
The pathogen Quambarleria coyrecup which causes the disease, was identified in WA in the 1970's; why are we seeing widespread outbreaks some 40 years later? I believe it is likely that the moisture stress experienced in the South West of our state, with declining rainfall since the 70's, has weakened these trees.
This is a pathogenic disease. Nature has a role for pathogens and it is to return carbon to the soil as quickly and efficiently as possible. Weak and stressed organisms send out signals which pathogens can identify and in they come to do their work.
Ebola spread is linked to a local practice in poor African societies of eating bush meat from flying foxes and apes. Ebola is a zoonotic disease that can pass from animal carriers where it has little effect through to humans where it had a catastrophic effect.
It is a widespread practice in WA to use raw greenwaste as mulch. Many councils offer this as free mulch to residents and many developers and landscapers apply this material to new housing developments.
The NSW Government have just legislated to stop this practice, greenwaste will have to be composted at least to the pasteurisation stage, before it can be applied to the soil.
C-Wise, a WA company with recognized expertise in the composting process, has been working with NSW local government to prove that a well-managed composting process, using mobile aerated floors, can provide cost-effective solutions that meet all of the NSW EPA’s requirements for control of pest, disease and vectors. This work has taken place over the last two years and was aimed at providing communities with methods to compost combined food and garden organic waste.
The aerated composting system used will easily meet the new requirements to process greenwaste. In fact, C-Wise and its customers around Australia have been doing this for years. The high temperatures kill off pathogens such as dieback and Gum tree Ebola. The controlled process ensures that a diverse range of beneficial microbes are encouraged to break down the ingredients and produce a stabilized form of carbon that builds soil health and can even help with disease suppression.
Just as with that other zoonotic tropic epidemic HIV/AIDS, the treatment that finally worked was boosting the immune system. How do you boost the immune system of a tree? Soil carbon is the key.
Soil carbon is food to the incredible diversity of soil living organisms. Plants are the only organisms that can capture carbon from the air and produce food from sunlight, air and water. So plants are the beginning of all food chains. The food from plants passes into the soil through roots and the breakdown of plant residues. The plants pass this carbon into the soil where it becomes food for a wide range of soil organisms. It takes some time for this to happen in nature.
WA soils have some of the world’s lowest carbon levels, sometimes only 0.5% organic carbon. If this level can be lifted to say 1.5% organic carbon you have a higher performance soil. Such soils have higher biodiversity which is one key to disease resistance and they are also highly suited to successful plant growth.
We can accelerate the building of healthy soils by adding carbon to the soil but not just any carbon. The carbon that really helps has been through a controlled composting process where it has been broken down and stabilized.
The recently amended Australian Standard for Compost and Mulches (AS4454) lists three stages of maturity. Maturity index 1 is pasteurised, index 2 is composted semi mature and index 3 is mature. The Index 3 composts are extremely stable, carbon rich materials that are the most successful at building effective soil carbon.
In my lifetime I have seen an explosion in tree diseases in WA . The first epidemic that came to my attention was Phytophthora or jarrah dieback. This has been described as an "ecological bulldozer" because of its devastating effect on a wide range of WA's wildflower species.
New species of Phytophthora have recently been discovered, we dont even know if they are pathogenic yet they are so new. The outbreak of gum tree Ebola is the most recent disease for me and is particularly worrying because the Marri tree is such a harbour of life in our forests and urban areas. Carnaby’s Cockatoo, a seriously endangered bird, feeds extensively on the gum nuts of Marri.
I urge anyone who is still spreading raw mulch to stop immediately. I would like to see a decentralised approach to composting these waste materials so that we keep the disease from spreading and at the same time work to produce quality soil carbon to help boost the immune system of our gardens and municipal plantings