Exotic nematode found in pine trees in Melbourne, Victoria
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Formerly known as the Forest Research Institute, Scion has been a leader in research relating to forest health for over 50 years. The Rotorua-based Crown Research Institute continues to provide science that will protect all forests from damage caused by insect pests, pathogens and weeds. The information presented below arises from these research activities.
From Forest Health News Special Issue, September 2000.
An exotic nematode, belonging to the genus Bursaphelenchus has been found in wood samples taken from a dying pine tree (Pinus halepensis) in the Melbourne suburb of Williamstown. The infested tree was removed and destroyed by the local city authority and the Victorian Department of Natural Resources and Environment. This is the first detection of a Bursaphelenchus in Victoria although other Bursaphelenchus spp. have been found in association with Ips grandicollis in Pinus taeda , and with other insects in Araucaria cunninghamii in other parts of Australia.
Bursaphelenchus xylophilus , the pine wood nematode, causes rapid death of pine trees and other conifers in Japan, Southern China, Korea, Taiwan, United States, Canada and has been recently detected in Portugal.
Bursaphelencus xylophilus is a native of North America. It does not adversely affect indigenous North American pines but has caused extensive losses in European pines (e.g. P. sylvestris) planted in North America. In Japan it has been responsible for widespread mortality of native Japanese pines, particularly P. densiflora and P. thunbergii. Many millions of dollars have been, and continue to be, spent on control measures by the Japanese government. This species, B. xylophilus , is not known to occur in Australia.
The Bursaphelenchus sp. isolated from the Victorian tree has been tentatively identified as Bursaphelenchus hunanensis , which has only been recorded from China. The incursion of a species such as B. hunanensis, raises the spectre of a similar scenario developing in pines originating in western countries. At this stage it is not known whether the Victorian Bursaphelenchus sp . is a primary (i.e. has caused the death of the tree) or a secondary pathogen of pines. Trials on seedling pines are being conducted to determine if the nematode is pathogenic to them.
Ground and aerial surveys (followed by sampling and testing), have identified 21 dead or dying pine trees containing the nematode (mostly Pinus radiata ). So far the disease appears confined to mature pines, possibly under stress when infested (tops of ridges, earthworks, poison etc.). The disease is distributed widely across Melbourne. Three of the 21 trees have so far been destroyed.
Symptoms of a Bursaphelenchus Infestation
Symptoms caused by Bursaphelenchus hunanensis are not well known whereas those of B. xylophilus (pine wilt nematode) are. Symptoms usually appear in late spring to early summer and develop over a four to six week period. Trees infested with this nematode generally wilt and die rapidly, although some may survive up to a year. Three to four weeks following infection the host tree's transpiration and resin production decreases. The tree's needles at first show a greyish green discoloration and then turn yellow-brown. Needles remain attached for six to twelve months before any defoliation occurs. Symptoms may develop simultaneously over the entire crown or one branch at a time may be affected. An important symptom is the reduction in resin flow. When the branches of a healthy tree are cut there is copious resin flow at the wound site. In infested trees there may be an absence of resin. Branches and twigs are also affected and become brittle, breaking easily.
Spread of Bursaphelenchus
Bursaphelenchus spp. are generally carried from tree to tree by wood boring insects. In the case of B. xylophilus the main vectors are species of Monochamus longhom beetles commonly referred to as pine sawyers. Monochamus species are absent from Australia and New Zealand. Many others species of wood- and bark-boring insects have been shown to carry B. xylophilus but none of them have been implicated in the spread of the disease.
In Melbourne no insect vectors have been identified. However, in some of the dead trees an introduced longhom beetle, Arhopalus rusticus , has been found. It is thought that this is the first time this Northern Hemisphere species, which was identified by John Bain at Forest Research, has been found in Australia. It is extremely unlikely that A. rusticus is a vector of the nematode because it does not feed or oviposit on live trees as do the species of Monochamus.
The spread of Bursaphelenchus species over long distances can occur through the movement of infested wood. If this wood also harbours suitable vectors then healthy pines can be infected when the insects emerge.
Species of Monochamus are quite frequent interceptions in casewood and dunnage but no instances are known of any of the species becoming established outside their natural range. However history tells us that there is a first time for everything! Pine dunnage and casewood from Australia harbouring live insects have been intercepted at New Zealand ports on many occasions.
The only available control is removal of the tree and either burning the wood or deep burial, to kill the nematode and any potential vectors.
How Can You Help
With the establishment of this nematode in Australia we need to be watchful for its accidental introduction into New Zealand. It is important to confirm early the presence of this nematode so that quick action can be taken to prevent its spread. If you suspect that a tree might be infested with a pine wilt nematode please take the appropriate samples and forward it to Forest Research. The most appropriate samples are:
- a 4-5 cm branch sample from near the trunk of the tree,
- a wedge of wood from low on the trunk, and
- a sample of a woody root taken close to the trunk.
Samples should be collected in a plastic bag and sent to:
Private Bag 3020
Attention: Forest Health
Web Sites about Pine Wilt
Kansas State University
Missouri Botanical Garden
Bain, J.; Hosking, G.P., 1988: Are New Zealand Pinus radiata plantaions threatened by pine wilt nematode Bursaphelenchus xylophilus ? New Zealand Forestry 32 (4): 19-21.
Geoff Ridley, John Bain and Margaret Dick, Forest Research
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(Scion is the trading name of the New Zealand Forest Research Institute Limited.)