Government of New Brunswick
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The fungus, Phytophthora erythroseptica, lives in soil and infects the underground parts of the potato plant. Disease development is favoured by high moisture and is found in low areas in fields.

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Wilting, which is sometimes the initial symptom, may occur at any time but generally occurs late in the season. Tubers usually become infected through stolons, eyes and lenticels (breathing pores). Infected tubers are dull brown, with darker brown eyes and breathing pores. The tuber rot develops with a visible dark line on the skin, indicating progress of the rot. Internal rot starts at the stem end and is creamy to light brown. If cut tubers are squeezed, a clear odourless liquid appears. On exposure to air, the colour of infected tissue progressively changes to pink, brown and black within an hour.

Control

Use healthy seed and avoid growing potatoes in the same field in consecutive years. Plant in well-drained soil. Rogue diseased plants. Grade out diseased tubers before storing crop.