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Infected dogwoods

Q: The leaves of my dogwoods are shriveled, and the trees never produce any berries. I have fertilized them and sprayed for borers, but they still look unhealthy. What’s the problem?

Sandra Lalley, Bridgeville, DE

A: Dr. Craig Hibben, former research plant pathologist at the  Brooklyn Botanic Garden  Research Center in Ossining, New York, replies: When the leaves of flowering dogwoods (Cornus florida) remain wet for more than several hours, these trees become susceptible to infection by the fungus Discula destructiva, which causes dogwood anthracnose. This infection progresses from the leaves to the branches, and finally into the trunk, resulting in shriveled leaves, cankers, branch dieback, and sometimes tree mortality. 

Because the fungus favors moist conditions, plant susceptible dogwoods such as C. florida in full to partial sun with good air circulation. For infected dogwoods, rake up and discard infected leaves and prune back diseased branches and trunk sprouts. Certain fungicidal sprays like chlorothalomil (professionally applied) will keep new leaves healthy. 

To avoid the problem altogether, plant anthracnose-resistant C. kousa or cultivars of C. X rutgersensis—a hybrid of C. florida and C. kousa released as the Stellar series by Rutgers University. ‘Aurora’, ‘Galaxy’, and ‘Ruth Allen’ are all noted performers. 

Two other possible causes of shriveling leaves and poor growth are waterlogged soils and bark injury. Damp soils harbor a type of fungus that enters through the lower trunk and roots, resulting in branch dieback and stunted growth. Bark wounds provide easy  entrance for soilborne pathogens. So, plant your dogwoods in well-drained soil and keep away from the trunk while mowing and trimming.

From Fine Gardening 66, pp. 86