Black Scurf, Rhizoctonia Canker
Pathogen: Rhizoctonia solani
Symptoms
 Irregularly
shaped black sclerotia, which cannot be removed by washing,
develop on the tubers. There can be additional symptoms: cracks,
malformation and depressions. Necroses at the ends of the
buds cause delayed budding, misshapen stems, and weak plants.
Brown cankers develop at the base and belowground portion
of the stem, and cause collapse of the stem, stunting, the
appearance of aboveground tubers, and, occasionally, severe
chlorosis of the top of the plant. A light-colored promycelium
develops at the base of the stem (the sexual stage of the
fungus).
Damage
Severe decreases in tuber quality and yield. The surface
of the tuber becomes covered with sclerotia in a variety of
sizes and shapes. There are occasionally cracks, depressions
and malformations of the tubers.
Conditions for Development
The fungus is maintained and transmitted by sclerotia on
the tubers and within the soil or plant residues. With optimal
conditions - 18oC - the
sclerotia germinate and penetrate stems, roots and stolons.
Development of sclerotia on tubers is pronounced in poorly
drained soils. Sclerotia development is accelerated from the
time of foliage destruction until harvest.
Control
Varieties: There are no resistant varieties.
Pesticides: Soil sterilization with metham-sodium and methyl
bromide, and tuber disinfestation (with rizolex, benzymidazol,
etc.).
Management: Using clean manure and disease-free seed tubers,
and limiting the amount of time the tubers are left in the
soil after defoliation. Aerial Stem
Rot
Black Dot, Colletotrichum
coccodes
Blackleg and Tuber Soft Rot
Black Scurf, Rhizoctonia Canker
Common Scab, Streptomyces scabies
Early Blight, Alternaria solani
Deep Pitted Scab, Streptomyces spp
Leak, Pythium ultimum
PLRV, Potato Leafroll Virus
Powdery Scab, Spongospora subterranea
PVX, Potato Virus X
PVY, Potato Virus Y
Verticillium Wilt, Verticillium dahliae
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