Department of Plant Pathology |
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| SWEET POTATO DISEASES |
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Black Rot is caused by the fungus Ceratostomella fimbriata. Symptoms appear on the foliage and on fleshy roots. The foilage appears yellowish and sickly. On fleshy roots, depressed circular spots of various sizes develop. The spots are grayish black when dry and greenish black when moist. A shallow dry decay extends about to the depth of the vascular ring. The black rot fungus overwinters in diseased roots and in soil. Disease development is promoted by moist soil conditions. |
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Scurf,
caused by the fungus Monilochaetes infuscans, affects only sweet potato. Scurf appears on fleshy roots as small brown superficial spots. The spots expand and coalesce, but remain superficial. In storage, affected tubers dry out and shrivel more rapidly than do healthy tubers. The scurf fungus overwinters in affected roots, in residue from affected vines, and in soil. Disease occurrence is promoted by wet heavy alkaline soil which contains abundant organic matter. |
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Streptomyces Soil Rot, also referred to as pox and pit, is caused by the fungus Streptomyces ipomoea. Symptoms begin as small dark dry surface spots. The dried tissue later falls out, leaving a pit or pox mark. Root growth around these spots is checked and, as other parts continue to grow, the root becomes distorted. Roots affected late, after most growth has occurred, become pitted but not distorted. The pox fungus lives, reproduces, and becomes prevalent in soil when sweet potatoes are repeatedly cropped. Disease occurrence is promoted by high pH. |
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Surface Rot
is caused by Fusarium oxysporum. Infection occurs late in the season, close to harvest. Surface rot spots are circular, slightly sunken, and lighter in color and more superficial than are the black rot spots. Disease is more prevalent in years when a wet period precedes harvest. In storage, moisture is lost through the spots and the roots shrink and become mummified. |
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