PESTS AND DISEASES OF FORESTRY IN NEW ZEALAND
Cyclaneusma delayed thinning trials
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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 61, March 1997.
In 1985, trials to test the effects of applying five different thinning ratios at five crop ages on the incidence of Cyclaneusma needle-cast were established on two sites at Kaingaroa Forest. Delayed thinning had a significant effect at one site. Plots that were thinned early when the disease was not apparent had higher disease levels - plots thinned at ages 4 and 5 had mean disease levels of 30.1% (disease severity exceeded 40% in 35% of the trees and their mean DBH was 351 mm compared to a mean DBH of 403 mm for the remaining 65% of the crop). In the plots thinned at ages 7 and 8 average disease severity was 11.1% (severity over 40% in only 7% of the trees). The early-thinned plots had lower DBH (384 mm) than the late-thinned plots (401 mm). Delayed thinning at the other site which had consistently low disease levels initially resulted in reduced growth, however the late-thinned plots outgrew the early-thinned plots during the 5-year period since final thinning in 1991, thereby eliminating any differences. Delayed thinning with selection for disease-resistant final-crop trees could be effective on sites suitable for Cyclaneusma development.
(Lindsay Bulman, FRI)
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