Farm Forestry New Zealand
PESTS AND DISEASES OF FORESTRY IN NEW ZEALAND
Pitch Canker - the Threat to Australasia
FHRC Project: 1997-03. Report - Pitch Canker – the Threat to Australasia. A Discussion Paper
Date: July, 1997
Author: M. A. Dick and J. Bain
Publication: Forest Research Project Record No.6111
Project reference: 1997-03
Executive summary:
Background
Pine pitch canker, caused by the fungus Fusarium subglutinans f. sp. pini is a serious disease of many species of pine and has been recorded from the USA, Haiti, South Africa, Mexico and Japan. It has proved to be particularly devastating to Pinus radiata in its natural range in California, where the disease was first reported in 1986. The fungus infects vegetative and reproductive plant parts of P. radiata of all ages. Shoots, branches, cones, seed, stems and exposed roots may all become infected. With the exception of seed, infected tissues become resin–soaked, developing a characteristic honey colour, and typically copious resin exudation occurs at the point of initial infection. Multiple branch infections may occur and dieback will generally spread within the crown prior to the initiation of stem infections. Mortality follows either girdling of the stem by several stem infections or attack by bark beetles attracted to stressed trees. Young trees (up to 4 years old) may wilt and die following a single basal infection at soil level and in these trees resin flow occurs on the stem at, or just above, the ground. Seedlings may develop root–rot typical of that caused by a range of common nursery soil pathogens, or damp–off if very young.
Naturally occurring and animal/insect caused wounds are required as infection courts for the fungus and researchers in California have found that most, if not all, new infections of P. radiata are insect–vectored. The primary vectors are species of several genera of bark, twig and cone beetles. Neither New Zealand nor Australia has any twig or cone beetles of pines. Two bark beetles (Hylastes ater and Hylurgus ligniperda) are common in both countries but are largely confined to trees less than 2 years of age. Ips grandicollis now occurs virtually throughout the pine growing regions of Australia but is less aggressive than the primary bark beetle vector of pitch canker in USA (I. paraconfusus) and will only attack stressed trees.
Observed field resistance of radiata pine is estimated at 15% of the population in California. This figure has been largely derived from urban and roadside plantings and may not reflect the situation in the natural stands. The disease is still moving into the 3 remaining stands and full realisation of the extent of natural resistance may be some years away.
All species of pines currently grown in plantations in New Zealand (Pinus attenuata, P. contorta, P. elliottii, P. muricata, P. patula, P. ponderosa, P. radiata, P. radiata x attenuata, P. strobus, P. taeda) have been found to be susceptible. Current indications are that P. radiata could be the most susceptible of those pine species exposed to the pathogen to date. Douglas fir (Pseudotsuga menziesii) is the only non–pine host.
The current state of knowledge of pitch canker disease, the potential for entry into New Zealand and the risk of establishment and spread was reviewed by Dick and Bain in the report presented to the Pitch Canker Workshop in November 1996. Since then further susceptible pine hosts from Mexico have been added to the list. In California the disease has continued to spread and has now been recorded in locations distant from the coastal fog belt where it had been largely confined since its introduction to the state.
A full assessment of the danger posed by pitch canker to the plantation forests of Australasia could not be completed by Dick and Bain because of some uncertainties about disease transmission and survival capabilities of the fungus. This document reviews the areas of uncertainty and proposes steps that could be taken to obtain that information. It also covers measures that could be implemented now to reduce the risk of entry of pitch canker. This disease is viewed as a potentially serious threat to plantation forests both by Australia and New Zealand and it is expected that any activities would be jointly funded by the two countries.
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