A preliminary hazard model of white pine blister rust for the Sacramento Ranger District, Lincoln National Forest

Blister rust, caused by the introduced fungus Cronartium ribicola, is a serious disease of white pines in North America. Since about 1970, an outbreak has been increasing in the Sacramento Mountains of southern New Mexico and threatens southwestern white pine. To help determine the expected extent and impact of blister rust, we propose a preliminary hazard model for the Sacramento Ranger District. The model is based on field observations and experience. We assume blister rust incidence and severity on white pine varies with microclimate and proximity to telial hosts (certain species of Ribes). We identify the sites at risk and rank them into three relative hazard classes based on elevation, plant association, and topographic position. Information is currently available to provisionally identify hazard for blister rust on 35% of the district area at risk. Of the area rated, 12% is low hazard, 43% is moderate hazard, and 45% is high hazard. Average rust incidence level for plots rated as low, moderate, or high hazard was 6%, 45%, and 47%, respectively; average severity was 0.1, 2.5, and 4.5 cankers per tree. Studies are underway to test and refine the model.