Plant Disease Management Handbook

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.

Cause An aphid-transmitted virus, potato virus Y, when combined with potato virus X.

Symptoms Little mottling is present, but leaves are decidedly wrinkled and curled. Individual necrotic spots start and progress until the leaf dies. Lower leaves die first; sometimes leaving a stem with a tuft of wrinkled leaves at the tip.

Cultural control

Image related to Potato (Solanum tuberosum)-Potato Rugose Mosaic

Note the necrotic areas on the leaflet midrib.

Photo part of OSU Extension Plant Pathology Slide

Shepody' with PVY and PVX.

Photo by Phil Hamm.

By K. Frost and C. M. Ocamb

See:

Potato (Solanum tuberosum) - Powdery Scab

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

Image related to Potato (Solanum tuberosum)-Potato Leafroll Virus (Leaf Roll)

Note the plant at the top of the picture with bronzed, rolled leaves.

Photo part of OSU Extension Plant Pathology Slide

Leaves curl up around the midrib and may assume a leathery texture.

Melodie Putnam, 2000.

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

Cause Phytophthora erythroseptica, a soilborne fungus-like organism. The disease is directly associated with high soil moisture. It becomes a problem in storage by encouraging the development and spread of soft rot. Pink rot does not spread in storage by spore movement but grows from tuber to tuber.