Pink rot – Phytophthora erythroseptica, fungus
This disease is favored by cool weather and wet or poorly drained soils. External symptoms may be noted at the stem end or around eyes and lenticels. The infected area turns purplish to dark brown, with a black band between diseased and healthy tissues. Infected tubers are rubbery or spongy and may exude a watery liquid when squeezed, distinguishing this disease from blackheart. When tubers are cut, the infected tissue turns pink in a matter of minutes and then progressively darkens to brown and finally black. The tubers may have a pungent odor resembling formaldehyde. The pink coloration after cutting is useful in separating pink rot from Pythium leak.
In addition, cavities do not develop in the flesh as with leak, and there is no dark border between diseased and healthy tissue on the inside of the tuber as occurs with blackleg and leak. The pathogen will spread in storage if the tubers are not kept dry. Because the pink rot organism is endemic in many soils, avoid planting in poorly drained areas of the field.