NOTES ON HYLPOXYLON CANKER OF ASPEN IN ALBERTA

The rate of canker growth, caused by HYPOXYLON PRUINATUM (Klotzsch) Cke. (H. MAMMATUM (Wahl.) Miller) and the intensification of the disease were investigated on trembling aspen, POPULUS TREMULOIDES Michx. in Elk Island National Park, Alberta. In 1963, 45.1 per cent of the trees on a 1/3-acre plot were either killed or infected. This number increased to 49.0 per cent during the following three years. All stem cankers were located below the 9 foot level and 75.0 per cent were facing north or northeast. The disease was not confined to a particular crown class. Infected, trees were killed in 4 to 8 years. Fifteen cankers were sectioned to study the nature of canker growth. The rate of girdling was not related to either the diameter or dominance of the tree. The cankers grew at a faster rate on dominant and co-dominant trees during the initial year of infection than on intermediate and overtopped trees. The disease did not cause increment loss during the infection period.