Back to Focus on Potato

Black Dot Root Rot of Potato
December 2010

By Dr. Barry Jacobsen
Professor and Extension Plant Pathologist
Montana State University
Bozeman, Montana
Phone: 406-994-5161

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Black dot has been proven to be both a widespread and important disease of potatoes. The causal fungus, Colletotrichum coccodes, is found worldwide, has a broad host range and can survive as sclerotia in soils for long periods. Yield losses of up to 40% have been shown for some cultivars in inoculated experiments with many commonly grown cultivars showing yield losses of 10-20%. Yield losses occur both through root rot and premature dying and from tuber blemishes that resemble Silver Scurf. Black dot is commonly involved in the early dying complex with Verticillium wilt and nematodes. Control of this disease can involve soil fumigation with Vapam or KPam, use of seed treatments such as Dynasty to prevent spread by seed, in furrow fungicide applications followed by post emergence fungicide applications, long rotations and production practices that reduce stress. While no cultivars are immune, cultivars with < 5% yield losses have been identified.

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