Kwanzan Cherry Diseases

Cytospora Canker

• Cytospora canker is a potential disease of ornamental cherry trees including Kwanzan cherry as cited by the University of Florida Extension site. The disease leads to the death of twigs and branches and is characterized by the appearance of slightly flat, dead areas on twigs and branches that gradually expand over time eventually breaking the branch. There is also a secretion of gum from the margins of the cankers during early spring. Cytospora canker is more common on the Kwanzan cherry trees under stress or those that are growing poorly. Management includes pruning and removal of diseased tree areas and avoiding wounding trees.

Black Knot

• The University of Florida Extension lists black knot as a potential disease of Kwanzan cherry trees. Black knot fungus, Apiosporina morbosa, produces black, warty, ½-inch to 1-foot galls on tree branches. Black knot is a common problem in 24 species of ornamental cherry trees. The disease causes infected twigs to die within a year of infection while the larger branches take longer to die. Infected trees grow less vigorously with declining overall health. Given the longer disease cycle, black knot is often overlooked in the early stages, getting more difficult to manage once it is established. Management includes pruning infected tree areas during winter, selecting trees with higher resistance and avoiding planting trees in areas with known disease problems.

Powdery Mildew

• Kwanzan cherry trees are liable to suffer from powdery mildew as cited by the University of Florida Extension site. Powdery mildew is a fungal disease possibly caused by a number of different fungi and lead to the appearance of white to gray powdery coating on the upper sides of the foliage. As disease progresses, other plant areas are also affected. In early stages, the coating is easy to rub off manually but, if left uncontrolled, it turns into a thick, mat-like growth that suffocates the plant tissues underneath it, leading to distorted foliage, buds and growing tips. Control options includes prompt removal and destruction of fallen foliage and using fungicides with potassium bicarbonate, neem oil and Bacillus subtilis.