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Lawsons cypress defoliation

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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.

Late in 1993 heavy defoliation of Lawsons cypress was observed at Slab Hut Creek, south of Reefton on the west coast of the South Island. The symptoms extended from the bottom of the tree crowns to mid upper crown level and appeared to affect all but the current years foliage in the upper crown. This gave the trees a scorched and sparse appearance, and since then a number of the trees have died. Although the majority of trees in any one stand are affected there are often individuals which retain full crowns. Inspection in the same area about a year earlier found the trees to be in good health with no observable defoliation.

Since the problem 'first' appeared at Slab Hut Creek similar defoliation has cropped up on both individual trees and in stands of Lawsons cypress from Westport to Hokitika on the West Coast and in a stand near Nelson, the latter suffering defoliation within the past six months. Defoliation varies slightly within affected stands but generally trees uniformly suffer 40-80% defoliation.

To date all the samples sent to FRI have consistently had the fungus Stigmina thujina isolated from the affected foliage.The forest health database has records of Lawsons defoliation associated with Stigmina thujina in the central North Island as far back as the mid 1980s, including samples collected from the grounds of FRI and the Kinleith mill. The fungus has also been isolated from samples collected within the last four years from individual Lawsons cypress trees at Lyttleton, Nelson and Wellington.

(Paul Bradbury, MoF)

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(Scion is the trading name of the New Zealand Forest Research Institute Limited.)


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