Azaleas are one of the most popular spring-flowering shrubs seen in landscapes. The disease is worse after plants have been stressed by extreme drought or heat. They are caused by the fungus, Exobasidium vaccinii. Eventually twigs may die back. 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. herald spring with a profusion of flowers in U.S. Department of Agriculture plant hardiness zones 5 through 9. Treatment with horticultural oil can help. Remove old mulch and replace with new in early spring. Up close, CMBS is white t… This shows spots on the branches of my azalea's. Informational table showing disease name, symptoms, pathogen/cause, and management of Azalea and Rhododendron diseases. Nutrient deficiencies are another common factor with azaleas. Bot canker, which is caused by the fungal pathogen Botryosphaeria dothidea, attacks woody parts of azaleas. Petal blight is caused by an airborne fungus which over-winters on the spent flowers. The adult female azalea bark scale is dark red with a long sucking mouthpart. Well-drained, organic soils with a pH of 4.5 to 5.5 are best suited for azaleas. Roots of affected plants appear soggy or blackened, and the outer portion of the root easily pulls away from the inner portion. * Reprinted by permission from Compendium of Rhododendron and Azalea Diseases, second edition, ISBN 0-89054-436-0 , published by the American Phytopathological Society. Feeding in groups, azalea caterpillars can quickly defoliate shrubs. Whiteflies do not respond well to treatment; however, neem oil may reduce populations. Azaleas (Rhododendron spp.) These insects may be seen on the lower surface of a leaf. Lacebugs feed by sucking chlorophyll from the leaves of many plants. Although the pest usually does not kill the host tree, it causes aesthetic damage, weakens the tree, and can cause honeydew and sooty mold to develop. Twig Blight – Twig blight may cause wilting and defoliation on one or more branches with a reddish-brown discoloration under the bark. 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. They live together symbiotically. Affected leaves may also curl up and drop. Since lichens are almost always found on weak plants, do lichens cause the plants to become sick? Rhododendron spp. Inappropriate watering can cause foliage to wilt, discolor, and drop. Insufficient watering is the primary contributor to plant stress that encourages this disease. Fungal leaf spot diseases can be caused by various pathogens, including Cercospora and Septoria species, and pepper leaves with unattractive stippling. Often the leaves are covered with a black fungus (sooty mold), which thrives on the honeydew or sugary substance excreted as the scale insects feed. If so, you have a fungus called powdery mildew. Crape myrtle bark scale is relatively easy to identify. While these attractive plants are generally hardy and problem free, they are occasionally bothered by pests and diseases. Pick off the leaves where the azalea leaf galls occur and dispose of them properly. Causal pathogens are Pythium and Phytophthora species fungi, which grow in the presence of poorly draining soils and overwatering. Azalea Bark Scale, Eriococcus azaleas, was discovered in 1881 and is a major yearly pest for Azaleas, Rhododendrons, and Huckleberries. White, cottony growths on leaf surfaces indicate the presence of this disease, which is usually controlled by using fungicides labeled for azaleas. Varieties of deciduous azaleas, including plumleaf azalea, pinxterbloom azalea and swamp azalea, are … Photo credit: A.L. Affected leaves eventually turn brown and should be removed and destroyed. Control with pruning and disposal of diseased branches, making cuts a few inches below discoloration. New growth is especially susceptible in early spring. University of California IPM Online: Azalea -- Rhododendron Spp. Azalea Caterpillars – These alzalea pests are reddish to brownish black with white and yellow stripes. Plants with heavy infestations eventually die. Wood discoloration when peeling back bark of an infected stem. And is it tied to the Spanish moss at all? Interestingly, a lichen is a “sandwich” made of algae in the center and fungus on the outside. Dark, sunken areas form around the openings and may spread laterally along stems. Bark and branches fall prey to this disease after fungi enter through natural openings or wounds. At certain times of the year, particularly during the summer months, you are bound to notice a plant or two in your landscape that has a black fungus growing on the leaves. Sign up to get all the latest gardening tips! Canker Diseases: Canker Diseases are caused by fungi that commonly enter the tree through wounds in the bark or branch stubs. Improper pruning can increase your risk of cankers. Loosening soil thoroughly on site and not planting azaleas deeper than they were in nursery pots are important for good drainage. Affected shrubs may be covered with sooty mold or appear as white, cottony masses within the forks of branches. 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. These branches should be removed and destroyed. 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On average, established azaleas require an inch of rainfall or irrigation per week during their active growing season. 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. Azalea. caused by the fungus Ophiostoma novo-ulmi. The white cotton-looking insects show up in limb and twig crotches. Spray with Thylate or Benomyl when blooms begin to open. Twig blight caused by the fungus Phomopsis can be a serious problem on well-established azalea plants. Some fungicides, such as triforine, may prevent diseases if you apply them before buds break. Powdery mildew more commonly attacks susceptible cultivars, such as “Hinodegiri,” and some deciduous azaleas. ... Lichens can also live on the bark of perfectly healthy branches, but there, it usually stays put. As a tradeoff for this striking display, azaleas must contend with a variety of fungal diseases that threaten their health and mar their beautiful blossoms. This fungus is a water mold, and thrives in poorly drained or wet conditions. Azalea Lace Bugs – These are one of the most common threats to azalea shrubs. Mildew, galls and leaf spots affect azalea foliage. First of all, take solace in the fact that their bark is worse than their bite. What to Do About Azalea Leaf Galls . Anthracnose – Leafspot and Dieback (fungus – Glomerella cingulata): Symptoms on leaves are characterized by numerous small, round spots on both leaf surfaces. As alien-looking and repulsive as azalea leaf galls are, they are not considered overly serious. Ask the Expert: what would get the white fungus off azaleas , leaf the azalea has white on them , on the leafs is it a fungus , what can spray on them will mild soapy water work. 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