|Discula destructiva Family: Gnomoniaceae
Common name: dogwood anthracnose
Host plant: Cornus florida (flowering dogwood); Cornus nuttallii (Pacific dogwood)
|Description & Life Cycle: This anthracnose fungus attacks the lower leaves of its preferred host tree and works its way up the tree to the uppermost leaves in a severe case of infection. Dogwood anthracnose is identifiable by its tan blotches surrounded by a purple rim. (The purple rim may not appear for a few days.) In some cases, the centre of the blotch area becomes so thin holes will appear within the purple rim.
Infected leaves on Pacific and flowering dogwoods usually drop prematurely in the spring. However, those leaves at the branch tips which may become infected in the fall will stay on the tree and cause the death of terminal buds. The result is a reduction of bud break in spring which forces the tree to produce new leaves through lateral buds in midsummer.
Flower buds and fruits are also susceptible to infection.
In the fall, any infected leaves typically stay on the branch allowing the anthracnose fungus to travel along the leaf petioles into the branch tips which results in oval-shaped cankers developing on the branches. These grow until the cankers completely girdle the branch, effectively killing it. If the fungus spreads to larger branches, these can also succumb to the infection…and if it reaches the main trunk, the whole tree can die.
This is a nasty fungus and, sadly, the cool, wet spring and fall weather we experience in the Pacific Northwest are exactly what Discula destructiva thrives on.
Special Notes: It is thought the dogwood anthracnose came from somewhere in Asia, arriving first in the Port of Seattle in 1976 and then in New York in 1978. From these two ports of entry, the fungus has spread into Washington, Oregon, Idaho, Connecticut, Massachusetts, New Jersey, Delaware, Pennsylvania, West Virginia, Virginia, Maryland, North Carolina, South Carolina, Tennessee, and Georgia. Two Canadian provinces, British Columbia and Ontario, also have the dogwood anthracnose fungus.
To give some scale to the seriousness of this fungus, a survey of Cornus florida trees was conducted in Catoctin Mountain National Park in Maryland in 1984, which determined only three percent of dogwoods were not infected with Discula destructiva. Four years later, a follow-up survey revealed eighty-nine percent of the dogwood trees had died, there were only a very, very few dogwood seedlings regenerating new growth in the forest, and all remaining live trees were infected.
Remedial Action: none known
Posted on March 22, 2018