OSU Extenison Plant Pathology Slide Collection, 1980.
Irregular, convex blisters form on the upper surface of leaves, while a yellow bloom develops on the underside of the blister.
Photo by Ralph S. Byther
Upper surface of the leaf puckers out from this disease.
Jay W. Pscheidt, 2008.
Cause The fungus Venturia populina is found on Lombardy poplar (P. nigra 'Italica') and eastern cottonwood (P. deltoides). The fungus Venturia inopina is found on black cottonwood (Populus trichocarpa) and on other Populus spp. in selections Tacamaha and Aigeiros and their hybrids.
Note the single shoot that has turned black and died back.
Photo by Jay W. Pscheidt, 1994.
Many leaves on these aspens are necrotic from Venturia infection.
Crown gall often occurs on roots as a solid mass of disorganized parenchyma cells.
OSU Plant Clinic Collection, 2011.
Crown gall on Populus angustifolia.
OSU Plant Clinic Image, 2014.
Cause Cytospora chrysosperma (sexual: Valsa sordida) has been reported from all three Pacific Northwest States, and Cytosporea nivea (formerly Leucostoma niveum) has been reported from Washington. Widespread and common on poplar, cottonwood, aspen, and willow; occasionally on mountain ash, maple, and cherry. Although the disease is found on many hosts, the fungi responsible may be host specific.
This poplar has Cytospora canker.
Melodie Putnam, 2010.
Cause Pseudomonas syringae pv. syringae, and/or P. s. pv. populus, bacteria. This is one of the limiting factors in seedling production in the Pacific Northwest. Fluctuating temperatures at or below freezing can intensify symptoms. The disease has been attributed to frost damage in the past.
Note the necrotic areas on the leaves and some shoot dieback.
Photo by Jay W. Pscheidt, 1994.
Leaf spots and shoot dieback can occur with this disease.
Photo by Carrie R. Foss
Bacterial canker on Aspen.
Melodie Putnam, 2008.
Many leaf spots on lower leaves on this Aspen.
Melodie Putnam, 2009.
Cause Rhizoctonia solani, a soilborne fungus favored by high greenhouse (soil) temperatures. Root rot increases as soil temperatures between 62°F and 79°F. It generally causes loss during rooting and can enter cuttings through wounds. Wounds from salt accumulation at the soil line also can be entry points. It survives in the soil as sclerotia or as mycelium colonizing bits of organic matter. The fungus can form knots of mycelium that develop into sclerotia.
These 'Euro Red Glory' plants had brown roots, root tips decaying, cankers at the base and wilted suddenly. Rhizoctonia sp found in addition to fungus gnat feeding.
Many powdery mildew colonies on leaves and bracts.
OSU Extension Plant Pathology Collection.
Cause The poinsettia mosaic virus is found in many plants throughout the industry. The virus can be transmitted mechanically but not by plants' simply touching each other. Transmission can also occur by using infected stock for propagation and grafting.
Symptoms Infected plant leaves develop angular areas of light and dark green. Bracteoles may be malformed and may not develop their full coloration. Symptoms may not occur at high temperatures.
Infected plant leaves develop angular areas of light and dark green.
