This disease causes rhododendron and azaleas to first have white powder-like spots on young leaves, which can spread to the entire upper and lower surfaces of the leaf. Victoria Lee Blackstone is a horticulturist and a professional writer who has authored research-based scientific/technical papers, horticultural articles, and magazine and newspaper articles. Botrytis blight, which is caused by the pathogen Botrytis cinerea, causes spotting or discoloration on flowers, rotten buds or buds that do not open. Rhododendron spp. A:That crusty growth might look like a fungus or mold, but it’s actually a bug called azalea bark scale. ), Clemson Cooperative Extension: Azalea & Rhododendron Diseases. 4 through 6). This fungus is a water mold, and thrives in poorly drained or wet conditions. Whiteflies – These pests usually occur in groups on the undersides of leaves, which turn yellow or die. These spots quickly enlarge, becoming soft and watery. Sign up for our newsletter. Blackened branches, covered by a sticky soot and white, cottony fluffs in the crotches of the lower branches are all symptoms of one of the most dreaded of azalea diseases. Leaf scorch, which is caused from too much sun, may appear as yellow or brown spots on foliage. Nutrient deficiencies are another common factor with azaleas. The bushes are often covered with sooty mold, a black fungus that grows in the honeydew excreted by the azalea bark scales as they feed. * Reprinted by permission from Compendium of Rhododendron and Azalea Diseases, second edition, ISBN 0-89054-436-0 , published by the American Phytopathological Society. Powdery mildew more commonly attacks susceptible cultivars, such as “Hinodegiri,” and some deciduous azaleas. Under severe conditions, the spots may coalesce and form large irregular spots. Bot canker, which is caused by the fungal pathogen Botryosphaeria dothidea, attacks woody parts of azaleas. Control with pruning and disposal of diseased branches, making cuts a few inches below discoloration. However, like other azaleas and rhododendrons, Encore azaleas may develop leaf infections caused by a variety of fungal pathogens, including azalea bark … Plants with heavy infestations eventually die. Fungicides are used t… It is spread mostly by winds. Death of branches with split bark may not occur until weeks or months after the injury. As cankers girdle twigs or branches, they cut off nutrient transport and woody parts die. Find more gardening information on Gardening Know How: Keep up to date with all that's happening in and around the garden. Stunt Nematode – These azalea pests attack the feeder roots and cause azalea plants to become stunted and yellow. The disease is worse after plants have been stressed by extreme drought or heat. Plants may exhibit discoloration with fewer or undersized foliage and flowers. They are caused by the fungus, Exobasidium vaccinii. The algae makes food from sunlight and air; the fungus protects the algae and supplies moisture. Lacebugs feed by sucking chlorophyll from the leaves of many plants. The adults are 1/8" long, flattened, and dark brown or black. Cloudy, overcast weather conditions cause favorable conditions for the disease to occur. Azaleas (Rhododendron spp.) This is a fungus that causes root death and damage to the bark tissue at the base of the trunk. Well-drained, organic soils with a pH of 4.5 to 5.5 are best suited for azaleas. herald spring with a profusion of flowers in U.S. Department of Agriculture plant hardiness zones 5 through 9. Treatment with horticultural oil … The azalea bark scale, Eriococcus azaleae Comstock, can be found on a variety of hosts grown in nurseries and landscapes including azalea, rhododendron, andromeda, hawthorn, poplar, willow, and most recently, it has been found infesting blueberries in the Pacific northwest. Azaleas are one of the most popular spring-flowering shrubs seen in landscapes. Flower blight, caused by the pathogen Ovulinia azaleae, also causes flower spots as well as collapsed blossoms. They live together symbiotically. https://www.giroudtree.com Azalea Bark Scale can destroy beautiful Azalea shrubs. To treat, eliminate the insects and prune any dead or dying parts of the plant. caused by the fungus Ophiostoma novo-ulmi. Insecticidal soap is usually effective in controlling lace bugs in late spring or fall. Up close, CMBS is white t… When crushed, these scales exude pink “blood”-like liquid. Canker Diseases: Canker Diseases are caused by fungi that commonly enter the tree through wounds in the bark or branch stubs. Wood discoloration when peeling back bark of an infected stem. Remove old mulch and replace with new in early spring. Dying leaves and stems. Azalea Bark Scale, Eriococcus azaleas, was discovered in 1881 and is a major yearly pest for Azaleas, Rhododendrons, and Huckleberries. Bookmark. Azalea bark scale. Diseased leaves may drop prematurely. Informational table showing disease name, symptoms, pathogen/cause, and management of Azalea and Rhododendron diseases. Rust – Rust is a fungal disease that causes reddish to orange spore masses on infected leaves, as well as galls or cankers on bark, which may occasionally kill the entire plant. © Copyright 2020 Hearst Communications, Inc. Causal pathogens are Pythium and Phytophthora species fungi, which grow in the presence of poorly draining soils and overwatering. Powdery Mildew – This azalea disease appears as white powdery growth on the leaves and occurs most often during fall. Removal of affected plants may be necessary. Scales are unusual insects. When cared for properly, the landscape plants liven up the garden for many years. Prevention of root and crown rots is the best management for these diseases, starting with planting azaleas. Many people enjoy the color and patterns lichens create. Whiteflies do not respond well to treatment; however, neem oil may reduce populations. Some of the more common azalea plant pests include the following: Azalea Bark Scale – This azalea plant pest occurs most often in the eastern United States. Also known as Botryosphaeria dothidea, or Phomopsis, and often starts with fungus infecting one branch. Azalea Bark Scale (Eriococcus azaleae) Bark scales are a type of soft scale and an infestation is indicated by clear sticky honeydew with attendant sooty mold (black fungus) on leaves or stems, yellowing of leaves, and twig dieback. Photo credit: A.L. Prune and dispose of infected leaves and shoots immediately. Both floral diseases are spread by splashing water that catapults fungal spores onto plants. These insects may be seen on the lower surface of a leaf. 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