Canker diseases—Botryosphaeria, Cytospora, and Nectria spp. and others
Most common canker disease pathogens are fungi. Many plant species are susceptible to Botryosphaeria, Cytospora, and Nectria cankers. More host-specific canker diseases include those infecting Chinese elm, cypress, pine, sycamore, and walnut.
A canker is a localized dead (necrotic) area on branches, trunks, or roots. Cankers vary greatly in appearance but are often a circular or oblong lesion that may be discolored, oozing, or sunken. Cutting under cankered bark usually reveals discolored tissue, which may have a well-defined margin separating it from healthy tissue. When cankers entirely circle (girdle) stems or trunks, foliage turns yellow or brown and wilts as the plant dies outward or upward from the canker.
Bacterial blight and canker, mechanical injuries (e.g., equipment impact and pruning), sunburn, and sunscald are other common causes of cankers.
To manage canker diseases, do not plant species that are poorly adapted to local conditions. Botryosphaeria canker of giant sequoia, Chinese elm anthracnose canker, and cypress canker of Leyland and Monterey cypress are virtually unavoidable when their hosts are poorly located; planting other species or resistant cultivars is the only practical management strategy.
Many canker diseases primarily damage plants that lack proper cultural care. Keep plants vigorous to avoid and limit these diseases. Prune dead and dying branches when they are first observed, making the cuts in healthy wood below any apparent cankers, and use good sanitation to avoid spreading canker pathogens on contaminated tools.
Pine pitch canker on Monterey pine
Cytospora canker sunken lesion
Brown canker margin under bark