Farm Forestry New Zealand
PESTS AND DISEASES OF FORESTRY IN NEW ZEALAND
'Measles' of eucalypts
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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 75, June 1998.
Small, roughly circular lesions on the green stems of several eucalypt species (dubbed 'measles' by some eucalypt growers) have aroused some interest of late. Several samples, particularly of Eucalyptus nitens , have found their way to the laboratory for examination. The lesions are usually quite shallow and a proportion will disappear altogether as the bark begins to flake and peel away. Others remain visible but the dead tissue does not penetrate sufficiently far into the stem to pose a problem. Several different fungi can be isolated from such lesions but the most common is Cytospora eucalypticola.
Cytospora eucalypticola is a widely distributed fungus (Australia and South Africa) and associated with a variety of cankers and branch/stem disorders of a range of eucalypt species. In inoculation tests it does not generally prove to be pathogenic, or only mildly so. It appears to readily colonise wounds caused by other agencies and may very probably take an active part in the stimulation of kino vein formation. One report from Australia states "Occasionally wounds inoculated with this fungus form small bark cankers. The fungus persists in the tissue, although the lesions heal rapidly." In South Africa it has been associated with the deaths of young, drought-stressed E. saligna. In Tasmania 14 eucalypt species (mainly E. nitens, E. regnans, E. delegatensis and E. obliqua) were surveyed in 1995-96 for fungi causing, and/or associated with, cankers or lesions. Twenty-nine fungal species were obtained and constituted 20.6% of the total (209) number of isolates. It was common on trees with crown dieback indicating other stress factors affecting the tree vigour. It was also frequently associated with dead branches in the lower shaded crown of E. nitens and E. globulus in young plantations throughout Tasmania.
In New Zealand we frequently find Cytospora associated with either dieback, cankering, or dead branches of eucalypt species although occasionally it looks as though there is a pathogenic attack. In one instance spreading lesions formed on the green stem of 4 year-old E. nitens , with the fungus sporulating nicely on the surface. However there was some lower branch death where the lesions were alongside or encompassing a branch, the stems did not become girdled and the fungus did not penetrate deeply enough into the tissue to do any damage.
More recently Cytospora was included in a series of inoculation trials at Forest Research during all 4 seasons, with 5 fungal genera, on E. regnans and E. botryoides . Other fungi showed varying degrees of pathogenicity (often differing according to season) but the wounds inoculated with Cytospora always healed over. I therefore generally view Cytospora as an invader of wounds or as a fairly weak pathogen. If it is the sole cause of the 'measles' I would not expect the fungus to penetrate sufficiently far into the wood to create a problem. But we haven't looked at very large numbers yet and there could be other causal agents of these symptoms.
(Margaret Dick, Forest Research)
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(Scion is the trading name of the New Zealand Forest Research Institute Limited.)
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