Kwanzan cherry trees provide fragrant, showy pink blossoms in the spring months, but these trees are short-lived because of the prevalence of disease. The U.S. Forest Service notes that Kwanzan cherries live 15 to 25 years on average. While some diseases can be managed, others will kill the tree.
Kwanzan cherry trees planted in a poor location can contract phytophthora root rot, which is often fatal to the tree. Early symptoms--where the roots begin to rot--occur underground so are not noticed. Later symptoms include dieback of twigs and branches, wilting and discoloration of foliage and darkening of the tree's bark. Trees can die suddenly or decline over a period of years. Gardeners should only plant Kwanzan cherry trees in well-draining soil and should avoiding overwatering, especially during periods of heavy rain.
Another oft-fatal disease that Kwanzan cherries can contract, Verticilium wilt shows its symptoms most often in summer. Foliage turns yellow or brown and wilts or curls. Often, this disease strikes a part of the tree, wilting an entire side while leaves across the canopy appear healthy. Kwanzan cherry trees may experience a one-time or chronic infection of Verticilium wilt. Gardeners should rake up fallen leaves so fungi doesn't overwinter in the soil. Fungicides have no effect on Verticilium wilt, but gardeners can attempt to control the disease with soil fumigants.
Powdery mildew causes cosmetic damage to Kwanzan cherries and weakens them but is not especially harmful. Foliage becomes coated with a white or yellow dust. Cool or humid weather brings on this fungal disease. Plant Kwanzan cherry trees in full sun, since powdery mildew dislikes sunlight. Treat affected trees with fungicides containing sulfur.
Trees afflicted with black knot develop long black galls on branches. Averaging 1/2 to 1 1/2 inches thick, the galls can grow up to 12 inches long. Branches often die back beyond the gall. Gardeners can control this disease by pruning off affected branches at their base and can spray the tree with a fungicide designed to treat this disease.