Cytospora canker—Cytospora spp.
Cytospora canker affects many plants, including birch, ceanothus, cypress (Italian, Leyland, and Monterey), fir, maple, poplar, redbud, stone fruits, and willow.
Identification
Cankers on major branches commonly appear as slightly sunken, smooth, roughly elliptical, reddish brown areas and sometimes exude copious resin. On poplar, C. chrysosperma causes sunken lesions that kill many small branches and twigs without forming any definite canker. Infected branches can turn brick-red in the spring, then fade to brown or tan by the fall.
There are many other common causes of cankers, including other species of canker fungi.
Life cycle
During moist weather, minute pimplelike or warty fungal fruiting bodies (pycnidia) may develop in infected bark. Pycnidia produce yellow to red tendrils, which are strings of asexual spores (conidia). When wet, huge numbers of conidia are released and dispersed primarily by wind and splashing rain.
Solutions
Drought stress and other disorders or pest damage dramatically increase most hosts' susceptibility to Cytospora canker. Provide appropriate soil moisture for species adapted to summer rainfall or riverbank environments if they are planted where summer drought prevails; irrigation should generally be deep and infrequent.
Avoid planting susceptible cypress in warm areas. Grow species that are resistant or not susceptible. Poplar hybrids that show some resistance to Cytospora include Easter, Mighty Mo, Nor, and Platte.
If cankers are limited to one or a few limbs, during the growing season, remove (cut out) cankers and destroy dead or damaged wood. Pruning during the growing season allows you to better identify branches with cankers. To ensure that all the disease is removed, cut several inches to one foot below any canker symptoms into healthy wood. Check the cut surface of damaged limbs to ensure that all the disease has been removed. Incomplete canker removal wastes time and is little to no benefit in disease management.
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Cytospora canker on corkscrew willow
Cytospora canker pycnidia (white) and spore masses (amber)
Cankered wood (top) incompletely pruned off
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