Plant Disease Management Handbook

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

Cause A phytoplasma transmitted by several species of leafhopper and within potato seed pieces.

Potato plant showing symptoms of an infection by a phytoplasma.

Photo by Ken Frost, 2017.

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

Image related to Potato (Solanum tuberosum)-White Mold (Sclerotinia Stem Rot)

Note the white mycelium along this stem lesion.

Photo by Paul Koepsell, 1979.

Note the dark sclerotium, characteristic of white mold.

Photo by Cynthia M. Ocamb, 1998

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.