Plant Disease Management Handbook

By P. B. Hamm and C. M. Ocamb

Image related to Potato (Solanum tuberosum)-Scab, Common

Note the roughened exterior of these tubers.

Photo part of OSU Extension Plant Pathology Slide Collection

Scab symptoms on a potato tuber.

Photo from OSU Extension Plant Pathology Slide Collection

Cause The alfalfa mosaic virus is carried in tubers, but aphids can transmit it from alfalfa plants to potato plants by feeding first on infected plants and then probing noninfected plants. Nearby alfalfa fields or volunteer infected alfalfa plants in potato fields can be a source of inoculum.

Symptoms Large, irregular, yellow to cream-color spots appear on leaves. Tubers may show internal brown necrotic areas.

Image related to Potato (Solanum tuberosum)-Calico

Note the yellow leaves symptomatic of calico disease.

Photo part of OSU Extension Plant Pathology Slide

Note the mosaic pattern in leaves.

Photo by Cynthia M. Ocamb, 1998.

Potato plant with calico symptoms.

Photo by Ken Frost, 2017.

Cause A physiological disorder associated with low moisture content of the tuber at harvest, bruising, low storage temperatures, and potash deficiency. Bruising increases rapidly when the pulp of potatoes being harvested drops below 47°F to 50°F (8.33°C to 10°C). Desiccation (pressure flatting) increases black spot when potatoes are handled.

Symptoms Internal black spots usually are at the tuber's stem end. White, smooth-skinned varieties are more susceptible.

Image related to Potato (Solanum tuberosum)-Black Spot (Internal Black Spot)

Photo by Phil Hamm

By K. Frost and C. M. Ocamb

Cause Colletotrichum coccodes, a fungus with a wide host range and present in many potato-growing regions.

Image related to Potato (Solanum tuberosum)-Black Dot

Foliar symptoms of black dot are similar to Verticillium or Rhizoctonia diseases.

Photo by Phil Hamm.

Notice here the black dot stem infections.

Photo by Phil Hamm

Notice the characteristic tiny, black sclerotia within the infected stems.

Photo by Phil Hamm

A tuber infected with black dot.

Photo by Phil Hamm

Close-up of an infected tuber with black dot.

Photo from OSU Extension Plant Pathology Slide Col

By K. Frost and C. M. Ocamb

Image related to Potato (Solanum tuberosum)-Bacterial Soft Rot, Blackleg and Lenticel Rot

Soft rot of potato tuber.

Photo from OSU Extension Plant Pathology Slide Col

Potato plant showing early wilting symptoms of blackleg.

Photo by Ken Frost, 2016.

Potato plant showing stem collapse due to blackleg.

Photo by Ken Frost, 2016.

Potato showing blackleg symptoms.

Photo by Ken Frost, 2017.

Note the black lesion at the stem base and aerial tubers on stems.

Photo by Phil Hamm.

Black leg symptoms are seen here on the potato stems.

Photo from OSU Extension Plant Pathology Slide Col

By P. B. Hamm and C. M. Ocamb

See:

Potato (Solanum tuberosum) - Purple Top

Image related to Potato (Solanum tuberosum)-Aster Yellows (Late-breaking Virus)

Note the yellow, curled leaves.

Photo by Paul Koepsell, 1983.

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Cedar, Port Orford (Chamaecyparis lawsoniana)

Cause The fungus Erysiphe adunca var. adunca (formerly Uncinula salicis) has been reported from British Columbia and the disease has been reported throughout the Pacific Northwest. Phyllactinia populi has also been reported from North America. Occasionally encountered on suppressed understory leaves of cottonwood and hybrid poplar.

Cause Drepanopeziza populi-albae (formerly Marssonina populi or M. castagnei) and M. piriformis, fungi, have been reported form Oregon. In British Columbia M. brunnea f. sp. trepidae, M. castagnei, and M. populi have been found.

Note the numerous leaf spots.

OSU Extension Plant Pathology Slide Collection, 1973.

Leaf spots are all due to Marssonina sp.

OSU Plant Clinic image, 2011.

See:

Maple (Acer spp.) - Leaf Scorch

Leaves have marginal burn and some so bad that only the leaf veins have remained green. Lack of water uptake due to black root rot in this case.

OSU Plant Clinic image, 2009.