Dogwood is a popular landscape tree throughout Kentucky, but it is not without its issues.
One major disease of dogwoods is powdery mildew. Its distinguishing feature is white powdery material on the leaves. However, the white powder may not always be present. Sometimes leaves just turn yellow with a faint tan area. Other times leaves have small, dark red splotches that appear on upper surfaces of otherwise healthy-looking leaves; later they turn dark brown.
Infection begins in early June and continues through September. High humidity makes the problem worse especially for young, succulent plant growth. The trouble with powdery mildew is that it reduces plant photosynthesis and increases leaf water loss, and over time weakens the tree. This can reduce flowering next year and make the tree more susceptible to other pest problems.
Fungicides are available to homeowners for control. Look for products with myclobutanil or propiconazole on the label. Ideally, fungicides should be started at the end of May and applied at three-week intervals through August to protect dogwoods from powdery mildew.
Other steps you can take to improve your dogwood health is to mulch under the drip line of the tree, remove dead branches and selectively pruning branches to increase air movement in the canopy. If you are thinking of planting a dogwood, choose trees with resistance to powdery mildew including "Jean's Appalachian Snow," "Karen's Appalachian Blush" and "Katy's Appalachian Mist."
Other dogwoods such as Kousa Dogwood and Cornelian Cherry Dogwood are immune to the disease.
Kelly R. Jackson is the Christian County Extension Agent for horticulture. He can be reached at 270-886-6328 or visit Christian County Horticulture online at www.christiancountyextension.com.