Development of comandra blister rust on lodgepole pine

Abstract

The comandra blister rust parasite (Cronartiumcomandrae Pk.) causes a serious canker disease of lodgepole pine (Pinuscontorta Dougl. ex Loud. ssp. latifolia (Engelm.) Critch.) in the central Rocky Mountains. The expansion, longevity, and distribution of comandra blister rust cankers were studied by annual monitoring, reconstructing canker histories, and random sampling. In saplings, infections occur throughout the lower 80% of the crown; and branch cankers expand toward the bole at 2.5 cm•year−1, regardless of temperature, age, position, tree size, vigor, or susceptibility to infection. The proportion of branch cankers that develop into stem cankers decreases logistically both with distance from infection site to bole and with time since infection. Fewer than 50% of branch cankers that are farther than 20 cm from the bole or more than 8 years old are expected to establish stem cankers. The proportion of branch cankers that become stem cankers decreases with distance more rapidly for comandra blister rust than for other stem rusts. The mean height of stem cankers increases with total tree height, but cankers are uncommon at the top of the crown and low on the trunk of larger trees. The number of years for a canker to girdle its host equals the diameter of the stem at the center of the canker measured in centimetres. Because girdling cankers develop infrequently, slowly, and predictably, potential losses from comandra blister rust can be reduced by timely and appropriate removal of damaged trees.