Pruning to manage white pine blister rust in the southern Rocky Mountains

Abstract

White pine blister rust is an exotic, invasive disease that se- verely damages and kills white pines in the southern Rocky Mountains. We evaluated the efficacy of preventive pruning (removing lower branches) and/or sanitation pruning (removing cankered branches) to reduce disease impacts in limber (Pinus flexilis James) and Rocky Mountain bristlecone (P. aristata Englm.) pine in two recreation areas in the southern Rocky Mountains. We compared the benefits of the different pruning techniques based on the distribution and severity of cankers, tree height class (small = 30 ft), and treatment feasibility and time. Preventive pruning removed less than half of all cankers at both sites. The most effective treatment, sanitation pruning, removed 98 to 100 percent of visible cankers. Cankers were located throughout tree crowns, and medium and tall trees had high incidences of cankers in the upper crown. Threatening cankers (cankers located on branches within 1 ft of or on the main stem) were common throughout the crowns of trees less than 30 ft tall. In 5 to 10 minutes per tree, crews reliably removed cankers up to 25 ft with ground based tools. Small and medium-sized trees will benefit most from pruning because nearly all threatening cankers can be removed with reasonable effort.