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Stem Canker and Black Scurf

Thursday, September 10th, 2009

(Rhizoctonia solani)

The fungus causing stem canker and black scurf is present in nearly all soils because it has a wide host range, survives in plant debris, and as sclerotia is easily disseminated on tubers.
It grows over a wide range of temperatures. It causes considerable damage to emerging sprouts when conditions do not favor rapid emergence, such as cold and wet soil.

Symptoms of stem canker and black scurf

stem-canker-black-scurfLesions on sprout tips cause delayed emergence or failure to emerge.

Slightly sunken brown cankers of variable size and shape affect stolons and stems at or below the soil line.
Cankers may girdle stems and result in aerial tuber formation, plant wilt, and death. Girdled stolons may fail to produce tubers.
Hard, dark brown or black sclerotia (fungus-resting bodies) of irregular size and shape form on the tuber surface.
A white mycelial mat may develop on the stem base, but does little harm to the plant.

Management

Because sclerotia are long-lived in the soil, while growing potatoes only long rotations with cereals and grasses reduce disease incidence.
Shallow planting of well-sprouted tubers reduces the exposure time of sprouts in the soil.
This potatoes disease can be reduced by applications of soil fungicides such as PCNB (pentachloronitrobenzene) mixed into the planting band of soil.

Potatoes seed tuber treatment effectively reduces seed-borne inoculum when soils are not heavily infested.

Trichoderma and binucleate Rhizoctonia used as biological control agents reduce severity.

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