Winter cold injury occurs after the plant has hardened and may affect buds, canes, trunks, and even roots. Winter temperatures between -10° and -17°F (-23° and -27°C) are generally critical for canes of American and French hybrid vines (Campbell and Ghosheh, 1957). Generally, when temperatures drop lower than -5°F (-20.4°C), winter bud injury should be assessed for American and French hybrid vines.
Familiarity with the compound bud of grape is necessary to evaluate the buds for winter injury. This compound bud actually consists of 3 single buds; the primary bud in the center, the secondary bud nearest the leaf scar, and the tertiary or smallest and least developed bud.