Rhododendron: Armillaria root rot categories: Ornamentals Rhododendron Rhododendron Diseases Shrubs revision date: 2022-12-05 12:00 White fungal mat of Armillaria root rot infecting trunkPhoto 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 flooded. Symptoms […]
Rhododendron: Botrytis shoot blight categories: Ornamentals Rhododendron Rhododendron Diseases Shrubs revision date: 2022-12-05 12:00 Botrytis shoot blightPhoto 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 on infected […]
Rhododendron: Gray blight categories: Ornamentals Rhododendron Rhododendron Diseases Shrubs revision date: 2022-12-05 12:00 Rhododendron gray blightPhoto 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 dark margins […]
Rhododendron: Leaf spot categories: Ornamentals Rhododendron Rhododendron Diseases Shrubs revision date: 2022-12-05 12:00 Rhododendron fungal leaf spotPhoto 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 bumpy on […]
Rhododendron: Lime-induced chlorosis categories: Ornamentals Rhododendron Rhododendron Diseases Shrubs revision date: 2022-12-05 12:00 Lime-induced chlorosis on rhododendronPhoto 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 on the […]
Rhododendron: Marginal leaf necrosis categories: Ornamentals Rhododendron Rhododendron Diseases Shrubs revision date: 2022-12-05 12:00 Rhododendron marginal leaf necrosisPhoto 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 (too much […]
Rhododendron: Physiological leaf spot categories: Ornamentals Rhododendron Rhododendron Diseases Shrubs revision date: 2022-12-05 12:00 Rhododendron physiological leaf spotPhoto 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 spot. One particularly […]
Rhododendron: Phytophthora blight categories: Ornamentals Rhododendron Rhododendron Diseases Shrubs revision date: 2022-12-05 12:00 Rhododendron Phytophthora blightPhoto 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 shoots, and […]
Rhododendron: Phytophthora root rot categories: Ornamentals Rhododendron Rhododendron Diseases Shrubs revision date: 2022-12-05 12:00 Phytophthora root rot on rhododendronPhoto 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, and even […]
Rhododendron: Powdery mildew categories: Ornamentals Rhododendron Rhododendron Diseases Shrubs revision date: 2022-12-05 12:00 Powdery mildew causing yellow spots on rhododendronPhoto 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. Leaves may […]
Rhododendron: Ramorum leaf and shoot blight (Sudden oak death) categories: Ornamentals Rhododendron Rhododendron Diseases Shrubs revision date: 2022-12-05 12:00 P. ramorum shoot blight symptoms on rhododendronPhoto 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 found in […]
Rhododendron: Rust categories: Ornamentals Rhododendron Rhododendron Diseases Shrubs revision date: 2022-12-05 12:00 Rhododendron rustPhoto 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 reveal characteristic […]
Rhododendron: Salt injury categories: Ornamentals Rhododendron Rhododendron Diseases Shrubs revision date: 2022-12-05 12:00 Leaf tip necrosis from salt damagePhoto 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 water can […]
Rhododendron: Sunburn categories: Ornamentals Rhododendron Rhododendron Diseases Shrubs revision date: 2022-12-05 12:00 Sunburn on rhododendron leavesPhoto by: R.S. Byther Biology Sunscald is caused by exposure of the leaves to bright sunlight during hot weather. Sunscalded leaves on rhododendrons generally have a yellow to brown blotch in the center. Often this blotch has a yellow halo […]
Rhododendron: Aphids categories: Ornamentals Rhododendron Rhododendron Insects Shrubs revision date: 2023-04-04 12:00 Aphid damage on rhododendronPhoto 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 by aphids, […]
Rhododendron: Azalea bark scale categories: Ornamentals Rhododendron Rhododendron Insects Shrubs revision date: 2023-04-04 12:00 Azalea bark scale and sooty moldPhoto 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 often located […]
Rhododendron: Caterpillars categories: Ornamentals Rhododendron Rhododendron Insects Shrubs revision date: 2023-04-12 12:00 Looper crawling on edge of rhododendron leafPhoto 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 and may […]
Rhododendron: Lecanium scale categories: Ornamentals Rhododendron Rhododendron Insects Shrubs revision date: 2023-02-09 12:00 Lecanium scales on twigPhoto 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, scale nymphs […]
Rhododendron: Rhododendron lace bug categories: Ornamentals Rhododendron Rhododendron Insects Shrubs revision date: 2023-04-04 12:00 Rhododendron lacebug symptoms on leavesPhoto 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″ long with […]
Rhododendron: Rhododendron whitefly categories: Ornamentals Rhododendron Rhododendron Insects Shrubs revision date: 2023-04-04 12:00 Rhododendron whitefly damagePhoto 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 on the […]