REVIEW
Relative importance of site, weather and Phytophthora cinnamomi
in the decline and death of Eucalyptus marginata – jarrah dieback
investigations in the 1970s to 1990s
E. M. Davison
1
Received: 18 March 2018 /Accepted: 23 April 2018 /Published online: 28 April 2018
#
Australasian Plant Pathology Society Inc. 2018
Abstract
Jarrah dieback was the name given to the sudden death of Eucalyptus marginata in the southwest of Western Australia, a serious
economic problem. Although deaths were attributed to Phytophthora cinnamomi in the 1960s, the supporting evidence was
weak; these deficiencies were not realised until 1980. Renewed interest in jarrah pathology showed that the incidence and
severity of root lesions caused by P. cinnamomi in live trees was low, but in recent deaths it could be isolated from the root
collar and large roots of some, but not all trees. Jarrah deaths result from hydraulic failure, implying extensive sapwood damage.
This is unlikely to result from P. cinnamomi infection, which preferentially invades phloem, but could result from waterlogging,
which causes tyloses to form in xylem vessels so they no longer conduct water. Tylosed root sapwood has been reported from
investigations into jarrah deaths. An interpretation of past deaths based on stress factors better fits where and when deaths occur.
This is within 3 years of exceptionally heavy rainfall, an inciting factor. Predisposing conditions are sites with some form of poor
drainage, such as water-gaining sites, or those with impeded sub-soil drainage. Recent logging further increases site wetness.
Phytophthora cinnamomi should be seen as a contributing factor, which is normally compartmentalised by the host, but can
spread extensively in dying trees.
Keywords Perched water tables
.
Phytophthora dieback
.
Selective reporting
.
Tolerant hosts
.
Tree excavations
Introduction
Jarrah, Eucalyptus marginata, is the most important timber
tree in the southwest of Western Australia. By the mid-
twentieth century it was also the most important timber
exported from Australia (Davison 2015). These exports were
threatened by the decline and death of jarrah trees, a problem
known as jarrah dieback, which occurred mainly between the
mid-1940s and mid-1960s. These deaths were jointly investi-
gated by the Western Australian Forests Department and the
Forestry and Timber Bureau in Canberra (FTB). In 1965,
Frank Podger (Research Officer, FTB) advised the Forests
Department that jarrah dieback was caused by the introduced,
soil-borne oomycete Phytophthora cinnamomi (Podger 1968,
1972). His explanation was accepted in good faith by the
Forests Department which immediately initiated a research
and management programme to control this pathogen
(Forests Department 1967). By the 1970s, phytophthora con-
trol dominated forest management in Western Australia.
In 1979 I was appointed to a position as mycologist/plant
pathologist in the Western Australian Department of
Conservation and Environment, to provide back-up to local
researchers working on jarrah dieback. This position was lo-
cated at Murdoch University. In 1980 as part of my review of
previous work, I found that Podger’s unpublished results did
not support his conclusion that P. cinnamomi killed jarrah
trees. Local researchers and forest managers were unaware
of this. Consequently, the Forests Department’s control mea-
sures may not have been as well targeted as they believed,
because an accurate diagnosis is essential for formulating ap-
propriate measures for disease management.
AreviewofhowP. cinnamomi became associated with the
death of jarrah trees has been recently published (Davison
2015). In this paper I briefly summarise the earliest work,
review the management of P. cinnamomi in the jarrah forest
during the 1970s, and comment on the renewed interest in
* E. M. Davison
e.davison@curtin.edu.au
1
School of Molecular and Life Sciences, Curtin University, GPO Box
U1987, Perth, WA 6845, Australia
Australasian Plant Pathology (2018) 47:245–257
https://doi.org/10.1007/s13313-018-0558-8
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