Plant Disease Management Handbook

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Onion (Allium cepa) - Downy mildew

Onion (Allium cepa) - Purple Blotch

Cause Several different fungi have been reported causing leaf spots in the PNW including Cylindrosporium sp., Rhopalidium cercosporelloides and Septogloeum schizonoti. The later has been found a few times by the OSU Plant Clinic. Powdery mildew has also been reported from Washington and Idaho. Pseudomonas syrinagae and Xanthomonas sp.

The bacteria Pseudomonas and Xanthomonas were associated with these leaf spots.

OSU Plant Clinic Image, 2013.

Hosts Poa annua and low-mowed bermudagrass (Cynodon spp.) in the PNW as well as creeping bentgrass (Agrostis palustris) in the southeast USA.

Other than the color, turfgrass does not have signs of abnormal growth.

Brian McDonald, 2012.

Spots stay in discreet infection centers.

Brian McDonald, 2012.

Yellow turf can expand up to 3 or 4 inches.

Brian McDonald, 2012.

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Tanoak (Notholithocarpus densiflorus) - Sudden Oak Death

Rhododendron - Ramorum Leaf Blight and Shoot Dieback

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Seed Crop, Crucifers (Brassica, Eruca, and Raphanus spp.) - Alternaria Diseases (Black Spot, Gray Leaf Spot, Pod Spot)

By C. M. Ocamb

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Cranberry (Vaccinium macrocarpon) - Botryosphaeria Fruit Rot and Berry Speckle

Leaf spots due to the fungus Calonectria (Cylindrocladium is the name for the asexual stage of the fungus).

OSU Plant Clinic, 2022.

Necrotic, circular leaf spots with a gray centers and brown to dark-purple boarder.

Sarah Lowder, 2018.

Small black fruiting bodies (pycnidia) may be seen in the necrotic area.

Sarah Lowder, 2018.  

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

These Impatiens have collapsed due to Rhizoctonia sp.

Photo by Stacy Fisher, 1990.

Poor looking pansy

Crown rot of Pansy due to Rhizoctonia sp.

OSU Plant Clinic Image, 2010.

This Sisyrinchium sp. root has Rhizoctonia root rot.

OSU Plant Clinic Image, 2019.

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Grape (Vitis spp.) - Black Foot Disease

Grape (Vitis spp.) - Botryosphaeria Dieback

Send samples into the Plant Clinic for diagnosis since each of the various trunk disease fungi may have very similar symptoms. This one grapevine had 4 different fungi including Phaeoacremonium, Botryosphaeria, Phomopsis, and Eutypa.

OSU Plant Clinic Image, 2016.

Cause The fungus Peronospora potentillae or similar species. The disease has been reported in Washington and found a few times by the OSU Plant Clinic. The cultivar Fire Storm is susceptible. Overhead watering favors disease development.

Symtoms of downy mildew on the top side (left) and bottom side (right) of the same geum leaf.

Plant Clinic Image, 2016.

Upper side of leaves may develop subtle angular purplish lesions (cultivar 'Tangerine').

Plant Clinic Image, 2014.

Cause Several different fungi have been found associated with rotted bulbs by the OSU Plant Clinic. The genus is described as having fragile bulbs that need to be handled carefully. Wounds are common entry points for bulb rotting fungi in other hosts. Different species are found in a wide variety of habitats from very dry to wet environments. Many species need dry conditions when dormant and/or during various periods in their development. Large bulbs develop a hole or hollow area in the center where the plant grew out then died back.

The discolored areas on these bulbs were due to Botryotinia sp.

Plant Clinic Image, 2012.