Cause A physiological disorder associated with low moisture content of the tuber at harvest, bruising, low storage temperatures, and potash deficiency. Bruising increases rapidly when the pulp of potatoes being harvested drops below 47°F to 50°F (8.33°C to 10°C). Desiccation (pressure flatting) increases black spot when potatoes are handled.
Symptoms Internal black spots usually are at the tuber's stem end. White, smooth-skinned varieties are more susceptible.
Cultural control
- Maintain a high potash level in soil.
- Maintain at least 50% of available soil moisture until harvest.
- Handle tubers carefully.
- Store at 40°F to 45°F. Warm to 70°F and hold 2 days before handling. Hold French fry and chipping potatoes at 47°F to 50°F.
- Maintain 95% relative humidity to prevent desiccation.