Cause There a number of fungi that can infect alder and result in stem decay and/or visible cankers. Few are economically important. Trunk rot is caused by Phellinus igniarius, which is reported to have some economic impact in timber, pulp, and recreation sites in British Columbia. Rough bark is caused by Didymosphaeria oregonensis and is thought to be limited to young trees. Canker growth stops as the bark thickens with age although rough bark remains on the trunks of mature trees. The gluing fungus, Hymenochaete agglutinans, kills the underlying cambium and forms cankers on live branches. Dead branches appear to be cemented to living branches giving the fungus its name. Silver leaf, Chondrostereum purpureum, is largely a saprophyte but can be a weak parasite. It has been considered as a candidate for use as a biological control agent for red alder stump sprouts. Hypoxylon canker, Entoleuca mammata, also occurs on alder but is more important on poplar and willow. Cytospora canker may also be found on alder on winter-injured tissue.
Symptoms Phellinus trunk rot produces a hard, woody hoof-shaped fruiting body generally called a conk. Its presence indicates a lot of decay. Internal decay is soft, yellow-white wood that contains fine black zone lines that run throughout and surround the decay column.
Rough bark forms bands on the stem that range from 1 to 60 cm in length. Around active edges of the lesions, dark perithecia develop. Young trees may be deformed if numerous cankers are present.
The gluing fungus appears as a yellow-margined brown felt on cankers.
Silver leaf decay in wood appears as a reddish-brown stain that disappears as decay advances. In advanced stages the wood is dry, lightweight, and white-mottled to pale yellow in color. Peak production of fruiting bodies was in the spring in BC. Leaves take on a silvery appearance rather than the normal green color.
Cultural control
- Keep trees in good vigor and avoid wounding.
- Remove and destroy dead or severely cankered branches or trees.
References Becker, E., Shamoun, S.F., and Hintz, W.E. 2005. Efficacy and environmental fate of Chondrostereum purpureum used as a biological control for red alder (Alnus rubra). Biological Control 33:269-277.
Cootsona, C. 2006. Identification and distribution of Neonectria major causing cankers on red alder (Alnus rubra). MS Thesis, University of Washington.