Plant Disease Management Handbook

Cause The fungus Puccinia sorghi (alternate host is corn) has been found on oxalis in Washington while Puccinia oxalidis (alternate host is creeping barberry) was found by the OSU Plant Clinic.

Symptoms Yellow to yellow-orange pustules (aecia) cover the leaves for P. sorghi.

Cause There are several fungal leaf spots reported on oxalis in the PNW including those caused by Ramularia oxalidis, Phyllosticta guttulatae, and Septoria oxalidis. Most fungal leaf spots such as these are favored by conditions that keep leaves wet for extended periods of time.

Leaf spot on wild Oxalis.

Jay W, Pscheidt, 2008.

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Prunus laurocerasus

See:

Wheat (Triticum aestivum) - Stem Rust (Black Rust)

Barberry (Berberis spp.) - Rusts

Numerous small spots are common on Oregon Grape in west side gardens.

Jay W, Pscheidt, 2008.

Note the yellow, reddish lesions causing the leaves to pucker.

Photo by Jay W. Pscheidt, 1994.

See:

Heavenly Bamboo (Nandina domestica) - Powdery Mildew

Image related to Oregon Grape (Mahonia aquifolium)-Powdery Mildew
Sometimes there are individual colonies, but a heavy, white growth develops on leaves by late in the season.
Photo by Jay W. Pscheidt, 2002.
Image related to Oregon Grape (Berberis aquifolium)-Powdery Mildew

Many leaves can become infected causing them to decline.

Jay W. Pscheidt, 2002.

Cause Many different fungi can cause leaf spots in the PNW. Phyllosticta sp. has been reported from Washington, and found by the OSU Plant Clinic. A survey in western Oregon found several fungi infecting symptomless leaves with Phomopsis sp. as the most prominent.

Image related to Oregon Grape (Berberis aquifolium)-Leaf Spot

Necrotic leaf spot where the unidentified fungus has produced small fruiting bodies in the tan area.

Bruce Rottink, 2015.

Coccomyces dentatus on dead leaf tissue forming polygon areas bounded by black lines.

Lorelle Sherman, 2022.

Coccomyces dentatus on dead leaf tissue with star-shaped fruiting bodies embedded in light gray areas bordered by black lines.

Lorelle Sherman, 2020.

See:

Maple (Acer spp.) - Leaf Scorch

Image related to Oregon Grape (Mahonia aquifolium)-Leaf Scorch

Young transplants, 100 F weather and little irrigation resulted in scorched leaves.

Jay W. Pscheidt, 2012.
Image related to Oregon Grape (Mahonia aquifolium)-Leaf Scorch

Heat related leaf scorch typically causes problems near the edge of leaves. These leaflets have turned red on the margin from 100 F weather.

Jay W. Pscheidt, 2012.

Cause There are over 27 viruses reported to infect orchids. The two most important are cymbidium mosaic virus, which has been found to infect 56 genera of orchids, and odontoglossum ringspot virus (formerly the orchid strain of tobacco mosaic virus), which has been reported from 20 orchid genera. Mixed infections of both viruses are common. Both viruses are transmitted by means not involving a vector: mechanical inoculation, division of infected plants, and contact between infected and healthy plants.

Cymbidium orchid with Odontoglossum Ringspot Virus.

OSU Extension Plant Pathology Slide Collection, 1983.

These leaf samples reacted positively to an ELISA test for Cymbidium Mosaic Virus.

Photo by Meloide Putnam, 1997

A bacilliform (rod-shaped) virus was found in this orchid leaf. Note the ring spot pattern.

Photo by Melodie Putnam, 1994

See:

Greenhouse Plants, Ornamental - Gray Mold

Cause Acidovorax avenae subsp. cattleyae (formerly Pseudomonas cattleya), a bacterium. Seedlings are infected through stomata, older plants through wounds. Bacteria in exudate spread from orchid to orchid by splashing water and from place to place with infected plants. Contaminated propagation tools are another way to transmit the bacteria. Warm, moist conditions and high nitrogen fertility favor the disease.

This bacterial spot occurred on a Phalaenopsis orchid.

Photo by Melodie Putnam, 1997