Pruning Western White Pine in British Columbia to Reduce White Pine Blister Rust Losses: 10-Year Results

Abstract

Abstract Survey lines were located in areas that had been pruned to control blister rust (Cronartium ribicola) 10 yr previously and adjacent control (unpruned) areas in 10 stands of western white pine. Stands were classified as densely stocked, moderately stocked, or open. Cankers were tallied and their position noted. The success of pruning varied from stand to stand. Since the stands had not been pruned at an early age, there was only a 4 and 5% reduction in threatening cankers and stem cankers respectively, as few new cankers were initiated. Stands with the greatest increase in cankering had Ribes spp., were open grown, or possessed a high component of small white pine. Repruning these specific stands may be worthwhile, but in general, entering stands again to do either pruning or scribing would produce few additional healthy trees. Doing both treatments, however, may significantly enhance the number of healthy stems. To optimize the benefits of pruning, stands should be entered early and pruning should continue until a sufficient number of stems are pruned to a height of 3 m to ensure full stocking. Other species may be impediments to spore movement within stands, and thus they should not be pruned. Dense stands initially had less rust than open stands and could be entered later, but once spaced, they also need to be pruned to 3 m to minimize rust infection. West. J. Appl. For: 13(2):60-63.