Frost or Cold Damage is a condition that exists when the air temperature near the earth’s surface drops below 0 ̊C. The temperature in which frost occurs depends with the crop species and cultivars. Frost damage in potato is likely to occur when the temperature drops to -2 ̊C or lower.

On foliage, frost causes burns and leaf withering. The worst affected leaves are usually the top leaves and the ones around the edge of the plant. In the case of young plants (5-10 cm), a severe frost can cause the green parts to wither completely. Growth recommences with the unaffected parts. Prolonged cold also causes a purplish discoloration of the edges of the leaflets. This formation of anthocyanin may be due to other stress factors such as deficiency or virus infection.

The symptoms on potato tubers appear after frost whereby the frozen part of the tuber becomes soft. The inside becomes liquid and blackens. In the case of partial frost irregular grey and black spots on the flesh commonly found on the outer part of the tuber.

Frost can also occur during storage at low temperatures that is close to 0°C for a relatively long period. Black and glossy tubers are some of the symptoms found prone to subsequent rotting after storage at low temperature, frost and oxygen deficiency. Inhibited sprouting marks may appear on the tuber necrosis and sometimes-depressed areas on the skin possibly with long hairy sprouts. Skin necrosis may appear when fine skinned cultivars are stored in low temperatures.

In order to improve the situation, it is advisable to plant using fertilizers containing high levels of Phosphorus and low levels of Nitrogen two weeks after the late freeze. A fertilizer with the formulation of 6-24-24 or 8-24-24 is highly recommended.

Source; http://ephytia.inra.fr/en/C/21109/Potato-Frost-or-cold-damage