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Disease Detection and Losses

Impact of Dothistroma Needle Blight and Armillaria Root Rot on Diameter Growth of Pinus radiata. Charles G. Shaw III, Scientist, Forest Research Institute, Private Bag, Rotorua, New Zealand, Senior author’s present address: Forest Sciences Laboratory, U.S. Forest Service, P.O. Box 909, Juneau, AK 99801, USA; Elisabeth H. A. Toes, Technician, Forest Research Institute, Private Bag, Rotorua, New Zealand. Phytopathology 67:1319-1323. Accepted for publication 19 April 1977. Copyright © 1977 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-67-1319.

The impact of Dothistroma needle blight (caused by Dothistroma pini) and Armillaria root rot (caused by Armillariella novae-zelandiae or A. limonea) on diameter increment at breast height of 8- to 10-yr-old Pinus radiata trees was measured with vernier-scale dendrometer bands. The sample trees were selected for similarity of means and variances in stem diameter and height before measurements began. Although infection by the fungi, either alone or in combination, did not alter the pattern of weekly or seasonal diameter increment, infection by D. pini alone was associated with a 17-73% annual loss in growth compared with noninfected trees and that by Armillariella alone with a 14-24% annual loss. Growth reduction in trees heavily infected by both fungi was greater than the sum of the losses attributable to heavy infection by each fungus alone. With Dothistroma needle blight, diameter growth was inversely related to the percentage of foliage affected and small trees grew significantly less than large trees with similar infection intensities. With Armillaria root rot there was no significant difference in growth between the two infection categories used (65-80% or >90% of the root collar expressing symptoms and/or signs of infection), but during the study year one-third of the severely affected trees died or were blown down by wind. Dendrometer bands were useful in quantifying losses in tree growth that are attributable to disease and that may affect forest management and productivity.