Freezing and chilling injury, nonpathogenic
Symptoms are somewhat variable depending on the temperature, exposure period, and potato cultivar. Externally, the tuber appears wrinkled and flabby, whereas internal tissues generally turn bluish grey to black in response to cold temperatures. Chilling damage to tubers occurs at temperatures below 38° F and appears as diffuse smoky grey areas inside the tubers. Blackening of the phloem, due to selective injury to this tissue, can also occur and closely resembles virus leafroll net necrosis. Tubers or portions of tubers that have been frozen at temperatures below 29° F are soft and watery. Frozen tissues tend to disintegrate and will eventually dry out. Symptoms of chilling and freezing can, but do not always, occur in the same tuber. Do not dig if a frozen crust is present on the ground. After a hard frost, discard any green tubers. Frost protection should be provided in storage and in transit.