Diseases of Potatoes: Powdery Scab

Powdery scab infection of potatoes occurs at tuber initiation. They are first visible as small pimples which later become brown. These brown visible pustules are filled with powdery masses of spore balls which in turn contain hundreds of cysts. In some potato cultivars, these powdery spore pustules can be very obvious. Symptoms sometimes develop on tubers after harvest. Early lesions on developing potato tubers are small and purple but if the tubers are set aside for a few days, spore balls will form under these lesions.

Russet varieties of potatoes may not show symptoms of this disease but in some potato cultivars the symptoms are obvious and render the tubers unmarketable. This disease shows up more readily in the wetter areas of the potato field.

Another unfortunate consequence of powdery scab in potatoes is the fact that this fungus-like disease can vector (spread) the mop-top virus. In fact, the mop-top virus survives in field populations of the powdery scab organism. Therefore, if a potato field has a mop-top virus infected powdery scab infestation, then potatoes planted in that field become infected with mop-top.

• Resistant cultivars to powdery scab - Russet Norkotah
• Moderately susceptible - Snowden, Atlantic, Superior, Katahdin and Russet Burbank
• Susceptible cultivars - Yukon Gold and Chieftan
• Highly susceptible - Kennebec, Norland and Shepody