Weeping cherry trees, known scientifically as Prunus Subhirtella, variety Pendula, is a graceful, ornamental tree favored for its long, sweeping branches and delicate pink springtime blooms. Unlike many other cherry tree varieties, the weeping cherry is reasonably resistant to disease. In spite of this, several diseases as well as certain insect infestations can cause health problems for weeping cherry trees.
Disease in weeping cherry trees can either be bacterial or fungal, with the majority of diseases being fungal. Bacterial diseases include leaf spot, twig cankers and X disease. Fungal diseases include black knot, gray mold, plum pockets and verticillium wilt. In some cases such as with X diseases, insects like leafhopper can spread the disease.
Twig cankers and black knot can be identified by small galls in the first year of infection. Following seasons will produce rapid growth of the gall into a lesion or a knot. Either disease will have the effect of girdling development and growth of the limb beyond the lesion or a knot. Gray mold starts as a browning of petals or leaves, usually in the center of the diseased tissue. When humidity rises, a grayish film spreads over the infected tissue, giving the disease its name. Leaf spot loosely describes several fungal infections that can present with various colors of spots depending on the source of the infection. Verticillium wilt begins with yellowing leaves, dieback or wilting of branches, and slow growth. Branches on one side of the weeping cherry tree may wilt all at once. Plum pocket affects young shoots which become deformed and curled. X disease reveals itself by changing leaf color to fall colors prematurely.
Galls and cankers begin to affect the tree in spring when weather is damp. Initial growth is slow but becomes rapid in the second year of the disease as galls become knots and lesions become larger. Mold and leaf spot also tend to begin in spring as moist, warm conditions are ideal for the fungus' growth. The disease continues to spread throughout the growing season unless treated. Verticillium wilt can appear anytime in the growing season but generally appears during the hotter temperatures of July and August. The disease progresses slowly in well-watered trees and more rapidly in stressed, poorly irrigated trees. Plum pocket releases spores in the spring that will overwinter in cracks and crevices, becoming active the following spring.
Treatment or Prevention
Fungal diseases are controlled efficiently by the application of fungicides except for verticillium wilt. Verticillium wilt is difficult to treat as it lives in the soil and can remain alive there for years. It is absorbed through the roots' water intake system. Soil fumigants are one option for its treatment. In addition to fungicide, the use of insecticide to prevent the spread of disease like X disease by leafhoppers is recommended.
Good maintenance practices will also help prevent many of the diseases of the weeping cherry. Remove fallen leaves and decaying plant material from under the trees where fungus can overwinter. When mowing, avoid damage to the trunk, which can allow insects and disease to penetrate. Buy disease-resistant varieties of trees and avoid planting in areas where disease has been present in the past. Irrigate the cherry tree well and fertilize annually to promote good health.
Fungal diseases take several years to cause serious damage. As they progress, the tree becomes stressed and weakened. Leaf spot or gray mold can eventually cause defoliation, which in turn, can deprive the tree of nutrients and bring about its death. Lesions and knots can girdle the branch they are on and cause it to die. Additionally, the wounds may provide openings that are inviting to insects, opening up another set of problems. Verticillium wilt is a serious disease that can bring about the death of the tree rapidly, depending upon other environmental factors.