Rate of increase of black-stain root disease in Douglas-fir plantations in Oregon and Washington

Spread of black-stain root disease, caused by Verticicladiellawageneri Kendrick, was monitored for 10 years in 27 infection centers in Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) plantations in western Oregon and Washington. The number of trees killed by black stain increased 4.4 times over the 10-year interval. Mortality increased 3.1 times in the first 5-year interval but only 1.4 times in the second 5 years. Infection centers expanded at an average radial rate of 0.9 m/year in the first 5 years and 0.4 m/year in the second, but only 31% of crop trees were killed within infection centers. The rate of disease increase within established infection centers decreased with stand age.