Plant Disease Management Handbook

By R. E. Ingham, P. B. Hamm, and C. M. Ocamb

Image related to Potato (Solanum tuberosum)-Verticillium Wilt (Potato Early Dying)

Note the wilted, chlorotic, dying leaves.

Photo part of OSU Extension Plant Pathology Slide

Note the tiny, dark microsclerotia produced by the fungus.

Photo by Phil Hamm.

Vascular discoloration is associated with Verticillium wilt.

Photo by Phil Hamm.

Vines prematurely yellow and die.

Mary Powelson, 1972.

Cause This physiological condition is caused by high temperatures and/or moisture stress during tuber development. Also known as sugar end or jelly end.

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

Image related to Potato (Solanum tuberosum)-Silver Scurf

Note the small, light-brown circular spots.

Photo by Phil Hamm.

Close-up of the affected area, showing conidia borne in whorls.

Photo by Phil Hamm.

Close-up of conidia.

Photo by Phil Hamm.

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

Image related to Potato (Solanum tuberosum)-Ring Rot

Note that the necrotic areas follow the vascular system of this tuber cut in cross section. Also note the cheesy exudate in the upper right necrotic area.

Photo by Kathy Merrifield, 1990.

External vs internal ring rot symptoms.

Randy C. Rowe

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

Cause Rhizoctonia solani, a fungus that is a common soil inhabitant and has a wide host range. Seed pieces can carry the fungus but soilborne inoculum can be equally as damaging.

Image related to Potato (Solanum tuberosum)-Rhizoctonia Canker (Black Scurf)

Stem lesions are characteristic of Rhizoctonia canker.

Photo by Cynthia M. Ocamb, 1998.

Black masses (scurf) can be seen on the tuber surface.

Photo from OSU Extension Plant Pathology Slide Col

Reddish-brown to brown lesions can be seen on stems, stolons, and roots.

Photo from OSU Extension Plant Pathology Slide Col

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

Cause A phytoplasma, also called BLTVA for Beet Leafhopper-transmitted Virescence Agent (a member of phytoplasma group 16SrVI in the PNW region). This disease caused substantial damage in 2002 in the Columbia Basin and additional damage during 2003. The main disease sources are infected potato seed, ladino clover, and perennial weeds. Aster yellows, which is not commonly found, cannot be separated from BLTVA without laboratory testing.

By A. Moore, K. Frost, and C. M. Ocamb

Image related to Potato (Solanum tuberosum)-Powdery Scab

Notice the scabby areas on the surface of the tuber, characteristic of powdery scab.

Photo by Paul Koepsell, 1988.

Scabby, warty lesions on a tuber infected with powdery scab.

Photo by Phil Hamm.

Lesions are filled with dark-brown spore balls (bottom left) that contain numerous resting spores (above).

Photo by Phil Hamm.

Cause The fungus, Golovinomyces orontii (formerly Erysiphe cichoracearum; anamorph Euoidium violae), is reported throughout the world on a wide range of hosts, but the strain on potatoes is a distinct physiologic race. Row-irrigated potatoes are more likely to show infection than sprinkler-irrigated.

Image related to Potato (Solanum tuberosum)-Powdery Mildew

Note the necrotic areas on this stem.

Photo by Kathy Merrifield, 1990.

Note the lighter coloration of some leaves. The white powdery coating typical of powdery mildew on most other hosts frequently does not develop on potatoes.

Photo by Phil Hamm.

Cause Synchytrium endobioticum, a primitive parasitic fungus that does not occur in the United States. Potato wart was found on Prince Edward Island, Canada in 2000, and there was concern that it may have spread to other areas. So far, the disease has not been found in other provinces of Canada or in the United States.

Image related to Potato (Solanum tuberosum)-Potato Wart

This tuber has developed a gall.

Photo by M. Putnam, 2001.

Notice the stem galling.

Photo by M. Putnam, 2001.