Farm Forestry New Zealand
PESTS AND DISEASES OF FORESTRY IN NEW ZEALAND
Dieback of one and two year-old Chamaecyparis lawsoniana
Scion is the leading provider of forest-related knowledge in New Zealand
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 78, September 1998.
Young Chamaecyparis lawsoniana planted in a number of locations have been exhibiting an unusual dieback of shoots over recent months. The disorder was first recognised in March of this year from samples collected by Paul Bradbury (MAF). First impressions were that the shoots had been nibbled off, leaving a tip of dead and discoloured tissue, and that the damage was insect in origin. After close examination by entomologists, supported by Paul's field observations, this theory was discarded. No pathogenic organisms were apparent on the affected material and, despite incubation in warm, humid conditions, isolation attempts from the diseased tissue did not yield any fungi or bacteria of note. Further samples were collected in April and in June for examination (both pathological and entomological) and were the same as the earlier samples from March.
Although affected plants are not dying, or even losing substantial amounts of crown, the loss of apical dominance through this tip death will lead to bushy, multi-leadered plants which will have little value or use as a timber tree.
Chamaecyparis lawsoniana do not generally recover well from loss of leaders and will simply develop as a bush (Paul Bradbury, pers. comm.)
Because of the uncertainty surrounding the cause of the disorder a proposal has been made to establish a biocide trial to resolve the issue. A 2-3 weekly application, over a few months, of broad-spectrum fungicides and an insecticide (selections made and recommended by John Ray, Forest Research) applied to several plots of new season (1998) plantings has been suggested. Duration of the continued applications would be dependent on symptom development in unsprayed control plots, but would probably be for about 3-5 months (approximately 6 applications). A trial of this nature should, at the very least, demonstrate whether the disorder is fungal or insect (or neither) in origin.
Samples were again collected in August 1998 and fruiting bodies of two species of Sarcostroma developed when the material was incubated in a damp-chamber. One of these species has previously been recorded in New Zealand, on Eucalyptus viminalis but was then associated with obvious insect damage. We have no records of the second species on any host plant. A Sarcostroma sp. has been isolated from the dying tissue of the August sample but it is too early to confirm if it is one of the two species that developed in the damp-chamber.
The genus Sarcostroma and the closely related Seimatosporium pose some difficulties in assigning specimens to species. The degree of variation in key taxonomic characters and the overlap between the descriptions of species means that species separation is fraught with pitfalls. Taxonomists have synonymised and then de-synonymised species at regular intervals. The genus Sarcostroma is recorded in many countries and a number of the species are plant pathogens, causing leaf lesions and/or twig or shoot cankers. Many others are saprophytes, or at best weak, secondary parasites causing insignificant damage to their hosts. The role of the two species found in this association is unknown.
Although there is no indisputable pathogen/pest to target at this stage, the disorder is one that has not been recorded previously by diagnosticians at Forest Research. The definitive cause(s) will only be determined from a further period of examination and study.
(Margaret Dick, Forest Research)
This information is intended for general interest only. It is not intended to be a substitute for specific specialist advice on any matter and should not be relied on for that purpose. Scion will not be liable for any direct, indirect, incidental, special, consequential or exemplary damages, loss of profits, or any other intangible losses that result from using the information provided on this site.
(Scion is the trading name of the New Zealand Forest Research Institute Limited.)
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