A Deadly Dogwood Disease
Dieback
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Infected foliage
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Dogwood trees are coveted for their beautiful, full round canopies and white bracted flowers that turn pink as they age. These popular urban trees look good all year round and are well-behaved, however, they do have a weakness: dogwood anthracnose (Discula destructiva). It’s a prevalent and destructive dogwood tree disease that’s a killer.
Lesions are brown haloed in purple.
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Dieback and infected foliage.
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Symptoms: Brown spots first appear on leaves and the flower bracts in the spring. Tan spot on the leaves have purple edges ringed with brown and soon the leaves become distorted. As the disease progresses all the branches and trunk are affected. Cankers (swollen or sunken brown areas) wrap around stems, cutting off circulation, killing the branch and even tree trunks. Infected stems die back at their tips leaving bare, dead branches.
Prevention: Wet, cold springs, shady locations and lack of air circulations prompt the disease. Plant dogwoods where they will receive good air circulation with no overhead trees, and don’t overcrowd. Locate them in full sun, especially in the morning to quickly evaporate morning dew. Avoid watering late in the day or in the evening and overhead watering. Avoid high nitrogen fertilizers and prune trees only in summer when it’s dry. Remove any infected foliage from the plant and the ground, especially in autumn. Don’t leave dead branches and foliage on the plant.
Prevention: Wet, cold springs, shady locations and lack of air circulations prompt the disease. Plant dogwoods where they will receive good air circulation with no overhead trees, and don’t overcrowd. Locate them in full sun, especially in the morning to quickly evaporate morning dew. Avoid watering late in the day or in the evening and overhead watering. Avoid high nitrogen fertilizers and prune trees only in summer when it’s dry. Remove any infected foliage from the plant and the ground, especially in autumn. Don’t leave dead branches and foliage on the plant.
Kousa dogwoods are highly resistant to anthracnose.
Select resistant varieties: The most susceptible dogwoods are indigenous to North America: Eastern flowering dogwood (Cornus florida) and the Pacific dogwood (Cornus nuttalli). The kousa dogwood (Cornus kousa), Appalachian Spring and Stellar Pink dogwood are highly resistant. Moderately resistant types are Celestial, Galaxy, Constellation, Ruth Ellen and Aurora. Inspect plants thoroughly before buying including their branches and trunk.
Dormant oil/lime sulfur combo offers some control.
Control: Although this disease is difficult to control, dormant oil and lime sulfur is helpful. This combination mix is sold together and must be applied when the tree is dormant, just before budbreak (late January to early February in the Pacific Northwest). Purchase the kit now as it is often not available in stores in the middle of winter. Follow the instructions and don’t forget to spray the ground surrounding the tree. For more information on dormant oil/lime sulfur click on Dormant Oil/Lime Sulfur. Copper fungicides have proven to be effective during the growing season. It is recommended to remove all infected leaves and plant parts from the plant and the ground before spraying.