Rhododendron: Armillaria root rot categories: Ornamentals Rhododendron Rhododendron Diseases Shrubs last review date: 2025-06-27 10:25 White fungal mat of Armillaria root rot infecting trunk Photo by: C.R. Foss Biology Armillaria root rot is a fungal disease transmitted between plants by root contact. Armillaria is often found in newly cleared soils or soils which have been […]
Rhododendron: Botrytis shoot blight categories: Ornamentals Rhododendron Rhododendron Diseases Shrubs last review date: 2025-06-27 11:10 Botrytis shoot blight Photo by: R.S. Byther Biology Botrytis shoot blight is a fungal disease found on shoots in early spring. Symptoms of infection include brown, water-soaked spots on the shoots and masses of gray spores which may be formed […]
Rhododendron: Gray blight categories: Ornamentals Rhododendron Rhododendron Diseases Shrubs last review date: 2025-06-27 11:13 Rhododendron gray blight Photo by: R.S. Byther Biology Gray blight is a fungal infection of the leaves. It usually becomes established after an injury to the leaf, such as sunscald, frost damage, or some mechanical injury. White spots or blotches with […]
Rhododendron: Leaf spot categories: Ornamentals Rhododendron Rhododendron Diseases Shrubs last review date: 2025-06-27 11:14 Rhododendron fungal leaf spot Photo by: R.S. Byther Biology Several fungi cause leaf spots on rhododendron. They often infect through wounds. Infected leaves display dark brown spots which may cover up to half of the leaf surface. These spots may feel […]
Rhododendron: Lime-induced chlorosis categories: Ornamentals Rhododendron Rhododendron Diseases Shrubs last review date: 2025-06-27 11:15 Lime-induced chlorosis on rhododendron Photo by: R.S. Byther Biology Lime-induced chlorosis, or leaf yellowing, is caused by alkaline soil conditions. High alkalinity of soils can make iron or manganese unavailable to plants, causing leaf chlorosis. Pale to bright yellow leaves, particularly […]
Rhododendron: Marginal leaf necrosis categories: Ornamentals Rhododendron Rhododendron Diseases Shrubs last review date: 2025-06-27 11:16 Rhododendron marginal leaf necrosis Photo by: R.S. Byther Biology Leaf scorch on rhododendrons is a response to stress. Symptoms include browning of tips or margins of leaves, with the damage sometimes spreading to the center of the leaf. Water stress […]
Rhododendron: Physiological leaf spot categories: Ornamentals Rhododendron Rhododendron Diseases Shrubs last review date: 2025-06-27 11:18 Rhododendron physiological leaf spot Photo by: R.S. Byther Biology Rhododendron leaves sometimes develop variously sized and shaped spots. These are usually dark purple in color. The exact cause is unknown, but cultural or environmental stress may result in physiological leaf […]
Rhododendron: Phytophthora blight categories: Ornamentals Rhododendron Rhododendron Diseases Shrubs last review date: 2025-08-20 07:14 Rhododendron Phytophthora blight Photo by: J.W. Pscheidt Biology Phytophthora blight is a fungal disease whose symptoms are often confused with chemical or mechanical injury or leaf scorch. Irregular dead spots on the tips or margins of leaves, shiny black cankers on […]
Rhododendron: Phytophthora root rot categories: Ornamentals Rhododendron Rhododendron Diseases Shrubs last review date: 2025-06-27 11:21 Phytophthora root rot on rhododendron Photo by: R.S. Byther Biology The symptoms produced by Phytophthora root rot are often confused with those caused by environmental or cultural problems. Above ground, infected plants may show stunting, yellowish-green leaves, branch dieback, wilt, […]
Rhododendron: Powdery mildew categories: Ornamentals Rhododendron Rhododendron Diseases Shrubs last review date: 2025-06-27 09:44 Powdery mildew causing yellow spots on rhododendron Photo by: C.R. Foss Biology Powdery mildew on rhododendrons is a fungal infection of the leaves. On rhododendrons, the disease often fails to develop the distinctive powdery white growth normally associated with powdery mildews. […]
Rhododendron: Ramorum leaf and shoot blight (Sudden oak death) categories: Ornamentals Rhododendron Rhododendron Diseases Shrubs last review date: 2025-06-27 09:50 P. ramorum shoot blight symptoms on rhododendron Photo by: M. Elliott Biology Ramorum leaf blight is caused by Phytophthora ramorum, the same organism that causes sudden oak death (SOD). In Washington, most cases have been […]
Rhododendron: Rust categories: Ornamentals Rhododendron Rhododendron Diseases Shrubs last review date: 2025-06-27 09:51 Rhododendron rust Photo by: R.S. Byther Biology Yellowish spots on the upper leaf surface and dark brown or purple spot on the lower leaf surface can indicate the presence of a rust infection. Later, the underside develops blisters which break open to […]
Rhododendron: Salt injury categories: Ornamentals Rhododendron Rhododendron Diseases Shrubs last review date: 2025-06-27 09:52 Leaf tip necrosis from salt damage Photo by: R.S. Byther Biology Salt injury to rhododendrons is typically a result of culture or environment. Excessive salt (mineral) levels in the soil or irrigation water, excessive use of chemical fertilizers, or lack of […]
Rhododendron: Sunburn categories: Ornamentals Rhododendron Rhododendron Diseases Shrubs last review date: 2025-06-27 09:53 Sunburn on rhododendron leaves Photo by: R.S. Byther Biology Sunscald is caused by exposure of the leaves to bright sunlight during hot weather. Sun scalded leaves on rhododendrons generally have a yellow to brown blotch in the center. Often this blotch has […]
Rhododendron: Aphids categories: Ornamentals Rhododendron Rhododendron Insects Shrubs last review date: 2025-06-27 09:54 Aphid damage on rhododendron Photo by: A.L. Antonelli Biology Aphids cause twisting, curling, or puckering of new growth by their feeding. Whitish cast skins and green live aphids may be visible on the undersides of leaves. Honeydew, a shiny, sticky substance excreted […]
Rhododendron: Azalea bark scale categories: Ornamentals Rhododendron Rhododendron Insects Shrubs last review date: 2025-06-27 09:56 Azalea bark scale and sooty mold Photo by: A.L. Antonelli Biology The azalea bark scale is a soft scale resembling mealybugs. Red females cover themselves and their eggs with a white, waxy protective coating. Cottony masses of the scales are […]
Rhododendron: Caterpillars categories: Ornamentals Rhododendron Rhododendron Insects Shrubs last review date: 2025-06-27 09:57 Looper crawling on edge of rhododendron leaf Photo by: S.J. Collman Biology Several caterpillar pests occur on rhododendrons, most notably cutworms, loopers, and the obliquebanded leafroller. Cutworms and loopers (various species) feed on leaf tissue, removing large, irregularly-shaped pieces. They are night-feeders […]
Rhododendron: Lecanium scale categories: Ornamentals Rhododendron Rhododendron Insects Shrubs last review date: 2025-06-27 09:58 Lecanium scales on twig Photo by: R.S. Byther Biology Lecanium scale adults are found on the twigs in late spring. At this stage they are usually brown or mottled brown and white bumps on the stems. During the summer and fall, […]
Rhododendron: Rhododendron lace bug categories: Ornamentals Rhododendron Rhododendron Insects Shrubs last review date: 2025-06-26 07:18 Rhododendron lacebug symptoms on leaves Photo by: C.R. Foss Biology The rhododendron lace bug causes stippling on the upper surface of the leaves, and deposits crusty or tar-like excrement on the lower surface. Adult insects are whitish-tan and approximately 1/8″ […]
Rhododendron: Rhododendron whitefly categories: Ornamentals Rhododendron Rhododendron Insects Shrubs last review date: 2025-06-27 10:01 Rhododendron whitefly damage Photo by: A.L. Antonelli Biology Whiteflies are small white insects that hold their wings rooflike over their abdomens rather than flat like true flies. Infested leaves, usually the tender young leaves at the branch tips, are mottled yellow […]