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Stigmina thujina - a needle blight of Lawsons cypress?

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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 70, December 1997- January 1998.

The earliest New Zealand record of Stigmina thujina in the FRI Mycology Herbarium dates back to 1963 when it was identified (as Coryneum thujinum , the then name for the fungus) on Chamaecyparis lawsoniana from Queens Gardens in Nelson. The fungus was first described from Thuja plicata in Oregon in 1924 but was not regarded as a pathogen of any note, and with any published references tending to be taxonomic in content. In 1971 a brief comment following a redisposition of the fungus to the genus Sciniatosporium simply stated "As far as it is known S. thujinum is restricted to Thuja plicata and occurs throughout most of the range of its host in the Pacific Slope region of western North America".

FRI records of S. thujina have accumulated slowly. The second chronological record, also on C. lawsoniana, was collected in Granville Forest in 1974 and the fungus was then not seen in the diagnostic laboratory until 1981. With one exception, on T. plicata, all records are on C. lawsoniana.

One report of serious defoliation of C. lawsoniana in association with S. thujina infection exists in the literature. In 1982 Hodges reported a needle blight of planted Lawsons cypress on several of the islands in the Hawaiian group. Severity of the disease within each group planting ranged from no symptoms to complete defoliation and death. The symptoms described are identical to those observed in New Zealand. Hodges concluded that differences in individual tree susceptibility were responsible for the variation in symptoms, as in several cases healthy trees were next to those which were heavily defoliated.

Chamaecyparis lawsoniana originates from coastal North America, as apparently the fungus does also, but there are no reports of defoliation associated with S. thujina from this part of the world. Although pathogenicity tests have not been carried out on Lawsons cypress, either here or in Hawaii, we have seen over many years a consistent association of this fungus with a particular set of symptoms, strongly suggesting a cause and effect relationship.

Taxonomic Note: The fungus is now looking for another name. In 1989 Sutton & Pascoe, deciding that the generic concept of was too broad, redefined the genus and excluded a number of species including Stigmina thujina. The assignment of the excluded species to either new or existing genera was left for others to do.

( Margaret Dick, FRI)

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