Pure stands of white spruce (Piceaglauca (Moench) Voss) have been decimated by dwarf mistletoe (Arceuthobiumpusillum Peck) in Sprucewoods Provincial Park. Infection ranged from 100% in some stands to 25% in stands invaded more recently. Large trees may live 40 years or longer after being infected. Trees with brooms, which previously had annual radial increments of 0.67 cm at 1.4 m, had annual increments in the last 5 years of 0.04 to 0.14 cm. White spruce less than 2 m tall were absent on all but one of the plots where the total number of seedlings decreased 20% in 2 years, and 24–27% of the surviving seedlings were infected. Dwarf mistletoe infection reduced annual height growth of infected seedlings 40% in 1977.