Dieback – The Biological Bulldozer

Written By Jayden O'Brien.
Undergrad. BSc. (Biological Sciences, Conservation Biology)

WHAT IS IT?

Dieback, a disease caused by the introduced fungus-like organism, Phytophthora cinnamomi, was first detected in W.A.’s South-west Forest’s in the early- 1920’s.  The organism is responsible for root rot in many plant species, including many native and introduced ornamental species. The fungus, originating from within Asia, was most likely introduced into Australia through European Settlement, which has now spread dramatically and it is estimated it infects hundreds of thousands of hectares of native vegetation in Western Australia, Victoria, Tasmania, South Australia and Coastal Queensland.

Phytophthora cinnamomi is a soil-borne organism often referred to as a fungus belonging to the Oomycetes or 'water moulds'. As the name suggests the pathogen depends on moist conditions that favour survival, sporulation and dispersal. The genus Phytophthora is pathenogenic, meaning that it causes disease in the process of extracting food from living plant tissue, which eventuates in the plant dieing shortly thereafter.

The fungus exists in 3 forms, that is, zoospores, chlamydospores and mycelium within its life cycle. However, the fungus is only pathenogenic in its mycelium form. In its zoospore (‘juvenile’) form, the P. cinnamomi are only capable of traveling short distances (25-35mm), but can be carried by moving water over large distances.  As they move through the soil, the zoospores are attracted to tips of plant roots, where they lodge, encyst and germinate to form mycelium. It is also possible that plant to plant contraction (of mycelium) may occur via root contact.

In their much larger, tougher, more abundant sporatic form, Chlamydospores (‘adult’) are produced in the plant roots in response to drying conditions.  From there they are transported in root fragments or soil particles until conditions are optimal for either more sporangia to be produced, or alternatively, mycelium to form and dieback continuing. 

DIEBACK AND 4WDRIVERS

That’s all good and well, but how does this affect us four wheel drivers?

A majority of our travels are on DEC (formerly CALM) managed land and privately owned property which could be possibly infected with dieback, without us knowing the slightest. Four-wheel drivers could unknowingly collect infected soil particles on the tyres and undercarriage of their vehicles and spread the disease to new (previously uninfected) areas. Dieback is a silent killer, and can be spread to those oblivious to the problem. Therefore, it is vital that we take some responsibility when out on our travels:

1. CHECKwith the local CALM ranger or office BEFORE entering a possible problem area. Most recent 4wd and touring books highlight possible and high-risk problem areas.

2. ALWAYS stick to well-established roads or tracks (where possible). ‘Bush Bashing’ is not only idiotic and irresponsible, but is prohibited in DEC operated areas and offenders can face penalties.

4. WASH your 4wd thoroughly (in a suitable area with proper drainage which is unlikely to spread to surrounding vegetation) after driving in possible dieback affected areas.

INFECTED AREAS?

In a nutshell, the area extends from as far north as Jurien right through to east of Esperance (south). Particular areas of high impact in Western Australia include the Jarrah forest (including Dieback risk areas within our catchments, i.e. ‘the Powerlines’) and the Banksia woodlands to the north & south of the Perth metropolitan area. Across the south-west most national parks are at risk, including the south-west Capes, tall timber forests around Manjimup, and south-coast national parks. For more information on the risk in areas you may be entering you should contact the local DEC office.

WHY BOTHER?

Simple! We all enjoy 4WDriving and more importantly, spending time in the outdoors, thus appreciate the views, aesthetics, and recreation our W.A. environment has to offer. Unfortunately, even though extensive testing is currently being done by the Research Centre for Phytophora (based in W.A.), there is no ‘cure’ for dieback as yet. Therefore it is up to us, to minimize our impact, so to limit the spread of dieback, and protect and conserve the environment for future generations.