The Oriental flowering cherry, also known as the Japanese flowering cherry (Prunus serrulata) is a member of the rose (Rosaceae) family. As its name implies, it is native to Japan. Its dramatic display of springtime flowers makes it popular as a lawn specimen or spaced along streets, where it generally grows to be 15 to 25 feet tall and 15 to 20 feet wide. Flowers are white or pink and emerge in early to mid-spring. Fall foliage varies from bronze to reddish to yellow-orange. Though beautiful, the Japanese flowering cherry tends to be short-lived because it is subject to a large number of pests and diseases.
Little Cherry Virus
Little cherry disease is a virus that originated in Japan and is spread by the apple mealy bug, which thrives on woody plant species. In fruiting cherry trees, the disease results in fruit that fails to mature completely; cherries will be small, pointed, pale and dull tasting. The disease attacks flowering as well as fruiting cherries, but the trees show no symptoms of disease. Little cherry virus is controlled with insecticide to kill the apple mealy bug.
Canker is a section of dead bark on a tree trunk or branch. It may be caused by mechanical means, such as abrasion by lawnmowers. Canker may also be caused by a fungal or bacterial infection that enters the tree at the site of a bark wound and grows slowly during the tree's dormant season. The tree then forms callus tissues at the edges of the infected areas during its growing season, which forms the canker. The infected area of bark may be cut out around its margins so that the tree can heal itself with new bark tissue.
Powdery mildew manifests as a powdery white coating on leaves. Caused by fungi, it begins, usually late in the growing season, as discrete white spots. These develop as they grow into a continuous coating. The fungus that causes powdery mildew favours humid conditions. Powdery mildew often results in stunting and distortion of leaves, buds and growing tips. Spread by spores, the fungus overwinters on infected plant parts and in fallen leaf debris. Control it by destroying fallen leaves in autumn and applying fungicide to affected trees.
Leaf Spot or Shot Hole
Leaf spot is caused by the fungus Blumeriella jaapii, which infects the tree during cool, moist spring weather just as new leaves are forming. The fungus reduces flowering and forms red spots on the leaves. The spots then rot, leaving holes in the leaves. When heavily infected, the tree's leaves turn yellow or brown and fall off prematurely. This weakens the tree, making it susceptible to winter injury. Treat leaf spot by removing and destroying all damaged foliage, removing dead branches to improve aeration and mulching well.
Cherry Green Ring Mottle Disease
Cherry green ring mottle disease is probably caused by a virus, but this has not yet been scientifically established. Symptoms include leaves growing downward; bark splitting; dieback, or shoots dying at the tips; and necrotic lesions, which are dead spots on leaves.
Phytophthora Root Rot
Phtyophthora root rot commonly occurs in heavy, poorly drained soils. It is caused by a soil-borne fungus that is spread by swimming spores. They travel through water-saturated soil and infect small roots. Once established in the roots, the fungus spreads through the inner bark into the lower stem region. Symptoms of an infected tree include leaf yellowing, wilting and browning, which may occur over the period of several years or suddenly. An infected tree often dies. Prevention measures include planting flowering cherry trees in well-drained sites, application of beneficial mycorrhizae to protect roots from infection and application of fungicide.
Black knot is caused by the fungus Apiosporina morbosa. It affects woody tissues, causing stunted growth and dieback. Infected trees produce few flowers, become weak and disfigured and may die. Fungus spores usually infect a tree in the spring, but symptoms, in the form of small swellings, usually appear in the fall. These enlarge to rough black knots over the winter. Smaller branches die off quickly, although larger branches may take several years to die. Black knot is managed by pruning existing knots, disposing of them and applying fungicide.
Silver leaf is a fungal disease caused by Chondrostereum purpureum. Toxins produced by the fungus sometimes cause a silvering of the leaves; in other instances the disease is characterised by twig and branch dieback. Diagnosis of silver leaf may be confirmed by pruning a branch of at least 1-inch diameter and wetting the cut surface. If the surface is stained brown, the tree is likely infected. Treatment for the disease is pruning off the infected limbs and burning them. There is no chemical control available.