Facing Spring Frost Damage in Grapevine: Recent Developments and the Role of Delayed Winter Pruning – A Review

In this review, we briefly discuss factors that increase spring frost risk in viticulture and provide updates on vine susceptibility to frost events and damage assessment. The core of the review describes a physiologically based tool to prevent frost damage by delayed winter pruning (done at or beyond the “wool” bud stage) to postpone budbreak. The exploited principle is related to the inherent acrotony of the grapevine, which would “sacrifice” the already-developing apical shoots to frost, while basal nodes are still dormant and thus preserved. A survey of 21 published papers confirms that final pruning, performed not later than when two to three unfolded leaves are borne on apical shoots, would delay budbreak by ~15 to 20 days, while yield is only mildly affected. At times, such a delay can carry on until harvest, postponing fruit maturity into a cooler time of year. Most recommended late-winter pruning protocols use a two-step intervention. In spurred cordons, a mechanical pre-cut that shortens canes to seven to eight nodes while also shredding wood can be made anytime during the dormant season. Thereafter, a final hand spur-shortening is made at a suitable developmental stage of the apical shoots. In a cane-pruned vine, previous year fruiting cane(s) can be removed any time in winter, while selecting at least two canes to keep vertical and longer than the required spacing-dictated length. Shortening of the two canes along with horizontal positioning should take place no later than when there are two to three unfolded leaves borne on the apical end of last season’s shoots.