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Disease Detection and Losses

Effects of Comandra Blister Rust on Growth and Survival of Lodgepole Pine. B. W. Geils, Research plant pathologist, United States Department of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station, Fort Collins, CO 80526; W. R. Jacobi, associate professor, Department of Plant Pathology and Weed Science, Colorado State University, Fort Collins 80523. Phytopathology 83:638-644. Accepted for publication 5 February 1993. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1993. DOI: 10.1094/Phyto-83-638.

Comandra blister rust, caused by the fungus Cronartium comandrae, reduced growth and survival of lodgepole pine trees (Pinus contorta subsp. latifolia) in the central Rocky Mountains. Stem analyses were used to determine annual increments of total cubic bolewood volume for 74 lodgepole pine trees 4–22 m tall, cankered by comandra blister rust. Mean annual increments after canker establishment were reduced 32% for trees with crown tops killed by comandra blister rust (spiked) and 9% for trees not yet girdled. Volume increments of spiked trees decreased each year after canker establishment until crown loss (top-kill) occurred; afterward, increments remained small and constant. Bolewood in spiked trees was sound but split and cracked above the canker. Reductions in radial increments for 140 spiked trees decreased with tree age when they were top-killed and increased with severity of crown loss, measured as the proportion of stem length above canker center. Total and sapwood basal areas, crown ratio, and basal area increment were highly correlated among spiked trees. Sixty percent of 2,070 trees on either temporary or monitored plots survived top-kill; percent survival increased with canker height. On 15 remeasured plots, no spiked trees with cankers higher than 13 m had died during the past 5 yr; trees with cankers lower than 13 m died at rates inversely proportional to canker height. Functions describing expected reductions in radial increment and survival can be incorporated into stand-growth and yield models to provide better estimates of disease effects.