Nursery Crop Science
Diseases to Watch Out for in Western North Carolina
Kelly Ivors
Department of Plant Pathology
NC State University
Ornamental diseases recently observed in western North Carolina will be highlighted during this talk, including newly identified diseases as well as diseases already known to the area. Some, but not all, of the diseases discussed are described below.
During the past 2-3 growing seasons, Passalora needle blight (also known as Cercosporidium needle blight) on Leyland Cypress has become widespread in North Carolina nurseries from the western mountains across the Piedmont. The severity of this disease became economically significant for a number of North Carolina growers in 2004, with the increased use of Leyland Cypress in the nursery, landscape and Christmas tree industry. Needle blight is now a widespread disease problem that threatens the future success of growing Leyland Cypress in the southeastern United States.
Botryosphaeria canker has also been frequently observed in western North Carolina on numerous nursery tree species. Botryosphaeria dothidea is an opportunistic fungus that infects stressed plants through existing openings, therefore it is important to protect plants by carefully avoiding all unnecessary wounding. This fungus can enter through wounds caused by winter injury, improper pruning, and wind and hail damage. Most healthy, vigorous plants are resistant to Botryosphaeria canker however environmental stress can readily predispose plants to attack.
Two destructive diseases have recently impacted flowering dogwood in the mountains. Dogwood anthracnose, caused by Discula destructiva, has severely affected large numbers of dogwoods in forest settings. The disease has also affected trees in nurseries and landscape plantings, but generally the impact is less devastating. Powdery mildew on dogwoods, caused by Microsphaera pulchra, is also a serious problem, resulting in reduced growth, deformation, and reproduction and death of small trees in nursery and landscape settings. This disease has led to additional production costs resulting from increased use of costly fungicides.
A newly identified disease of unknown etiology, currently termed ‘thread blight’, has also been identified on numerous ornamental tree species including Bradford pear, plum and maple. The disease gets its name because a sparse, white mycelial fan can be observed in advance of dead areas on partially blighted leaves. This mycelium can be traced as fine white threads back to the leaf petiole and twigs, and abscised leaves may be tied to twigs and leaves by this network of threads and mycelium. Symptoms are readily noticed in early summer as affected leaves wilt and turn brown, usually in the interior or shaded portions of the tree. Current research is underway to identify the causal agent of this disorder.
