DOGWOODS UNDER ATTACK
By Bailey Walten 1990 Newsletter
Our native dogwood, “CORNUS FLORIDA,” is at risk from the fungus “DISCULA,” an anthracnose fungus. Commonly known as lower branch die-back and decline, it first starts on the leaves with small purplish spots or larger tan blotches with purple rims. The same fungus can infect twigs which turn tan, dry out and die.
Watersprouts or suckers often are more prevalent on infected trees and they can be more blighted as well and provide an avenue to move the disease into the main trunk and branches. This results in killing off patches of bark that girdle the tree and reduce sap flow. Without preventive measures, a tree could die within a few years of initial infestation.
It is thought that environmental stresses have made dogwoods more susceptible to this blight. Dogwoods are particularly prone to drought being shallow rooted trees, so watering during Summer and Fall dry periods is extremely important. This disease has been especially bad in the Northeastern United States and appears to be moving south and becoming evident in our area. Dogwoods north of Baltimore City seem to be hit harder than those south of the City. This past Winter’s abnormally cold December followed by a mild January and February and then some severe frosts in Early Spring appear to have aggravated the situation, because we have seen a lot of dieback in branches where buds started to open and then were frost-bitten.
Long, cool, rainy Springs enhance the spread of the disease by promoting germination of fungus spores and spreading them branch to branch. As with other plant diseases, prevention is the best cure. Steps should be taken to strengthen the dogwoods by fertilizing regularly and watering during dry periods. Badly damaged trees should be cut down and removed from the property and salvageable trees should have blighted limbs pruned out during dry weather. Removal of fallen leaves in the Fall, a form of sanitation, will help reduce the spread of the disease. Fungicidal spraying of the foliage should be done 2-3 times in the Spring at 1 ½ – 2 week intervals, beginning at bud break. Controls are more effective if warm, dry weather conditions exist as leaves develop. Trials are currently being performed to test the effectiveness of injecting fungicides directly in the tree, thus reducing the incidence of treatment! The application of fungicides in the Fall to the buds has also shown positive effects.