Plant Disease Management Handbook

By C. M. Ocamb and D.A. Johnson

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Peppermint (Mentha spp.) - Nematode, Root-lesion

Image related to Peppermint (Mentha spp.)-Verticillium Wilt

Plants near the center have smaller, bunched and/or bronzed terminal leaves.

Photo by Paul Koepsell, 1978.

Note the shoot with wilting symptoms.

Photo by Cynthia M. Ocamb, 2003

This section of field shows plant die-out due to Verticillium wilt.

Photo by Cynthia M. Ocamb, 2003

Cause Several fungi that live in soil. Stolon decay is associated with Fusarium solani. Stem and stolon canker are caused by Rhizoctonia solani.

Symptoms Roots, runners, and rhizomes have brown or black progressively rotting areas. Stands may be greatly reduced, frequently in spots.

Cultural control

Cause The Impatiens necrotic spot virus (INSV) and the Tomato spotted wilt virus (TSWV) infect many economically important plants, including both dicots and monocots, and have been found in mint.

Image related to Peppermint (Mentha spp.)-Spotted Wilt

Note some leaves with yellow tips and necrotic spots.

Photo by Kathy Merrifield, 1990.

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

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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.

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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.

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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.

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.