Mortality of western white pine transplants used to assess resistance to blister rust at the USDA Forest Service Nursery in Coeur d'Alene, Idaho was likely due to extensive root infection by Pythiva app. Severity of foliar symptom production was significantly correlated with extent of root system colonization by these fungi. Soil populations of Pythiula were also related to disease occurrence which was most evident in poorly drained portions of beds. Although Fusariva oxysporua was frequently isolated from diseased transplants, its variable distribution in the soil and poor correlation with disease symptoms indicate that this fungus was probably not the major cause of the disorder.