Cause Cytospora chrysosperma (sexual: Valsa sordida) has been reported from all three Pacific Northwest States, and Cytosporea nivea (formerly Leucostoma niveum) has been reported from Washington. Widespread and common on poplar, cottonwood, aspen, and willow; occasionally on mountain ash, maple, and cherry. Although the disease is found on many hosts, the fungi responsible may be host specific. Isolates from aspen or cottonwood were not pathogenic on alder, ash, elm or willow but were able to infect each other. The disease can be serious, especially on Lombardy and silverleaf poplars. The fungi enter trees through wounds. Weakened trees are more susceptible.
Dothichiza canker, caused by Plagiostoma populinum (formerly Cryptodiaporthe populea), was found killing Lombardy poplar trees in Portland, OR in 2005 and in the Seattle, Washington area in 2013. The disease is widespread on Lombardy poplar in North America and Europe in landscape settings. Willow and Bolleana poplar are also susceptible while aspen and white poplar are tolerant. Infection occurs during wet weather in the winter on wounded tissue or in autumn via leaf scars. Very similar to Valsa canker.
Other important cankers on Populus spp. include Entoleuca mammata (formerly Hypoxylon mammatum) on aspen, and Ceratocystis fimbriata (target canker), none of which has been reported from the Pacific Northwest. However, other Hypoxylon spp. have been reported for Oregon and Idaho.
Symptoms Cytospora canker-Young twigs develop brownish, sunken, roughly circular areas in the bark. The fungus may grow down the twig and into larger branches on the trunk. Large cankers may be on branches and trunks. Infected bark discolors to orange or orange-brown and eventually darkens to black. This orange-brown bark discoloration is the most common and easily observed symptom and is frequently accompanied by an orange-brown liquid ooze. Pycnidia in the bark give the canker surface a pimpled appearance. Later, perithecial stroma develop in the dead, cankered areas. Twigs and smaller branches may die back without definite cankers.
Dothichiza canker-Cankers appear in all sizes and age classes of stems but most frequently on twigs and small branches, especially in branch axils. Dieback occurs when cankers finally girdle the stem. Tissue beneath cankers is discolored. Adventitious sprouts frequently develop below cankered areas and then become infected as well. Pycnidia are often found within the cankered tissue very similar in appearance to Cytospora canker.
Cultural control
- Keep trees in good vigor and avoid wounding.
- Remove and destroy dead or severely cankered branches.
Chemical control Fixed coppers may help in nursery production, but none is specifically registered for this crop.
References Booth, C., Gibson, I.A.S., and Sutton, B.C. 1973. Cryptodiaporthe populea. CMI Descriptions of Pathogenic Fungi and Bacteria, No. 364. Surrey, England: Commonwealth Mycological Institute.
Callan, B.E. and Ring, F.M. 1994. An annotated host fungus index for Populus in British Columbia. Canadian Forest Service FRDA Report 222. Victoria, BC: Pacific Forestry Center.
Kepley, J.B. and Jacobi, W.R. 2000. Pathogenicity of Cytospora fungi on six hardwood species. Journal of Arboriculture 26:326-332.