Plant Disease Management Handbook

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Apple (Malus spp.) - Nematode, Root-lesion

Cause Macrophomina phaseolina is a soilborne fungus that is favored by dry and warm soil conditions and has an extensive host range including beans, brassicas, clovers, corn, cucurbits, grape, lettuce, peppers, onion, strawberry, tomato, tree fruits, and conifers. Disease development is enhanced by high temperature, soil water deficit, and sandy soils. The fungus produces microsclerotia for long-term survival and dispersal in the soil.

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Tanoak (Notholithocarpus densiflorus) - Sudden Oak Death

Rhododendron - Ramorum Leaf Blight and Shoot Dieback

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Fir, Douglas and True - Web Blight

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Fir, Douglas and True - Laminated Root Rot

Note This is a serious disease of several conifers including mountain hemlock. Western hemlock may be infected but usually not killed.

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Hazelnut (Corylus avellana) - Eastern Filbert Blight

Diplodia canker on Jefferson hazelnut both surface view (left) and in cross section (right).

OSU Plant Clinic image, 2019.

Sunken looking Diplodia canker on hazelnut cultivar McDonald.

OSU Plant Clinic image, 2019.

Diplodia canker on hazelnut with fruiting bodies erupting from the bark.

OSU Plant Clinic image, 2017.

Phomopsis stem canker on Jefferson hazelnut.

OSU Plant Clinic image, 2019.

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Tomato (Solanum lycopersicum) - Powdery Mildew

Cause An unknown leaf spot is common in landscapes and gardens in western Oregon. The main symptom is a brown necrosis of the underside of the leaf that looks like a network of lines on the margins of the leaf spot. Spots may be numerous and generally occur between the leaf veins. Tops of leaves may show no symptoms at all or more subtle necrosis between the veins. Symptoms were not apparent when surveying in early June 2022 but by July spots were quite numerous on plants throughout OSU campus.

Netted leaf spot on underside of leaf with subtle injury on top.

Jay W. Pscheidt, 2012.

Although these spots look somewhat like ringspots it was negative for viral particles.

OSU Plant Clinic image, 2018.

The leaf damage is unknown but ozone is suspected due to the distribution of symptoms on plants and leaves.

OSU Plant Clinic image, 2012.

Note The fungus Phoma caricae-papayae (formerly Ascochyta caricae) has been reported from Oregon causing leaf spots. The OSU Plant Clinic has found the fungus Botrytis sp. and the bacterium Pseudomonas sp. associated with leaf spots.

Lots of unidentified leaf spots on these fig leaves.

Heather Stoven, 2019.

Note The fungus Diplodia sycina var. syconophyla has been reported from Oregon causing canker and dieback symptoms. Nectria cinnabarina has been reported from Oregon and found a few times by the OSU Plant Clinic. Botrytis cinerea, which can cause a stem blight, has been reported from Washington. These fungi do not seem to be a common problem in the PNW.

Not that several shoots on this fig tree have died back with new shoots arising below the damaged tissue.

Anonymous.