Issue 7, June 4, 2010
Cryptodiaporthe Canker of Pagoda Dogwood
Pagoda dogwood is one of the most beautiful dogwoods available. The species, Cornus alternifolia, has a distinct horizontal branching pattern that is accentuated by the flat topped cymes of white flowers in May.
Although resistant to most diseases, pagoda dogwood usually succumbs to Cryptodiaporthe canker when it reaches the ripe age of 20-25 years. Cryptodiaporthe canker is also known as the golden canker, due to the yellow-orange color of infected bark. The fungus causes dieback of twigs and cankers of larger branches, as seen in the image. As far as we know, Cryptodiaporthe corni only attacks pagoda dogwoods (Cornus alternifolia). More importantly, it seems to be present in trees that are stressed from heat and drought. As is the case with many canker fungi, Cryptodiaporthe continues to spread when the tree is dormant, killing girdled branches. When the trunk is infected, tree death usually results. It is likely that spores of the fungus are present on orange cankers in the spring, but the infection cycle is not well understood.
To manage this disease, use sound horticultural practices to keep your pagoda dogwood healthy. This species does best in partial shade with moist, well drained soil. Slightly acidic conditions are best. Some dogwoods can tolerate exposed, dry sites, but pagoda dogwoods in such locations will likely succumb quickly to Cryptodiaporthe canker. Irrigate in periods of drought to help tree vitality.--Nancy Pataky