Estimating Spread of Pori Weirii in a High-Elevation, Mixed Conifer Stand

Poria weirii root rot pockets in high-elevation, mixed conifer stands appear on aerial photographs as irregular rings. Using 1972 and 1946 photos, progress of the disease was measured on 10 infection centers. Annual extension over the 26-year period averaged 34 cm in radius. Relative growth rate, on malt agar, of P. weirii clones isolated from individual pockets did not appear to be correlated with measured rate of disease enlargement of those pockets.