Spring frosts and subsequent crop losses threaten the economic sustainability of fruit crop producers all over the world. This study used a controlled-freezing technique to impose a post-budburst freezing stress to grapevine shoots forced from one-node cuttings [’Albariño’, ‘Cabernet Franc’, ‘Cabernet Sauvignon’, and ‘Pinot Grigio’ (Vitis vinifera)] and whole plants [’Noiret’ (Vitis hybrid)]. Our goal was to investigate the incidence of freeze injury among cultivars, stage of phenological development, and a potassium salt-based fertilizer (KDL) with potential cryoprotectant activity. Among the V. vinifera cultivars, the incidence of mortality of shoots exposed to - 3.5 °C was highest for ‘Albariño’ (71%) and lowest for ‘Cabernet Sauvignon’ (51%). Cuttings sprayed withKDL 24 hours before cold temperature exposure exhibited 16% lower shoot mortality and lower osmotic potential (Ψs) (-0.92 MPa) than the unsprayed cuttings (-0.77 MPa). However, application of KDL did not impact shoot mortality for whole ‘Noiret’ vines. Mortality for ‘Noiret’ shoots greatly increased with the advancement of phenological development, ranging from 10% in wooly buds to 78% in shoots ≈ 10-cm long. The practical significance of KDL remains questionable; cultivar selection still appears to be a more reliable method for avoiding spring frost, by planting late bursting cultivars in more frost-prone areas.
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