Plant Disease Management Handbook

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Image related to Poplar (Populus spp.)-Crown Gall

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.

Image related to Poplar (Populus spp.)-Canker

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.

Image related to Poplar (Populus spp.)-Bacterial Blight

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.

OSU Plant Clinic image, 2013.

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Greenhouse Plants, Ornamental - Pythium Seed Rot, Damping-off, and Root Rot

Image related to Poinsettia (Euphorbia pulcherrima)-Pythium Root Rot

Above ground symptoms may be general from poor functioning roots.

OSU Plant Clinic Image, 2013.

Brown mushy roots occur after infection.

OSU Plant Clinic Image, 2013.

Close-up of brown roots with Pythium.

OSU Plant Clinic Image, 2013.

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Greenhouse Plants, Ornamental - Powdery Mildew

Image related to Poinsettia (Euphorbia pulcherrima)-Powdery Mildew

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.

Image related to Poinsettia (Euphorbia pulcherrima)-Mosaic

Infected plant leaves develop angular areas of light and dark green.

OSU Plant Clinic Image, 2014.

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Greenhouse Plants, Ornamental - Gray Mold

Canker in the middle of the stem caused by Botrytis.

Oregon State University Plant Clinic image, 2020.

Image related to Poinsettia (Euphorbia pulcherrima)-Gray Mold

This stem canker is caused by Botrytis cinerea.

Photo by Melodie Putnam, 1997.

Lesions are often noticed first on the edges of young leaves and bracts.

Photo by Melodie Putnam, 1992.

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Dracaena - Tip Burn

Note: Domestic water that contains chlorine and/or fluoride is usually not harmful to poinsettias. Toxicity of fluoride at >0.4 ppm in the water results in necrotic spots on the tips and margins of young leaves and bracts.

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Greenhouse Plants, Ornamental - Black Root Rot