Powdery Scab
Pathogen: Spongospora subterranea
Symptoms
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The disease causes severe blemishes (2-20 mm diameter) on
the tuber. These blemishes contain dark-colored spore balls
that spread beneath the epidermis and erupt when the tuber
emerges. In severe cases, the tubers are malformed and covered
with unattractive secondary growths. If the plant is also
infected with mop top, which can be transmitted by the fungus,
deep cracks appear. Roots may also be affected with gall formation.
Damage
Severe malformation of the tubers. Spores can survive in
the soil for years. Contaminated propagation material is unusable.
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Conditions for Development
The spores develop under conditions of high humidity, poor drainage,
and temperatures of 16-20?C; they persist in the soil and infest
the young tubers via zoospores. Penetration occurs through the
open lenticles. Tomato and other solani spps can also serve
as hosts and infest the soil. The spores survive in the digestive
systems of animals.
Control
Pesticides: Fumigation with methyl bromide or other
agents effective for soil sterilization. According to the
literature, disinfesting tubers with caspan or formaldehyde
effectively controls the pathogen on the seed tubers.
Management: Use of disease-free propagative material;
prevention of over-watering, particularly in heavy soils;
use of manure or compost that does not contain spore balls. 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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