Crop yield effects on cold hardiness of 'Cabernet Sauvignon' dormant buds

Grapes grown in the mid-Atlantic region of the USA face many challenges, including that of low temperature injury. Mid-winter low temperature injury can be expressed as dormant bud kill, destruction of vascular tissues, particularly phloem and paratrachial xylem parenchyma, and complete vine loss. Outside of appropriate vineyard site and cultivar selection, the grower must apply prudent cultural practices to minimize the threat of cold injury, in part, by minimizing vine stress. Crop level was investigated over a six-year period with field-grown 'Cabernet Sauvignon' grapevines to determine how crop level affected dormant bud and cane cold hardiness. Annual crop levels approximated either 9 or 18 Mg/ha. The higher crop slightly reduced the fall acclimation rate of dormant buds in three of the six seasons, with significant differences typically appearing only in November. Mid-winter dormant bud cold hardiness, the extent of cane maturation, and cane cold hardiness were generally unaffected by crop level. The data illustrate that a slight penalty is paid for high crops as evidenced by a delay in the cold acclimation rate of buds in fall. The slower acclimation rate was apparent even when vines were not measurably stressed using conventional indices of cane pruning weights, fruit sugar accumulation rate, or degree of cane maturity. The delayed acclimation may be tolerable in regions with an extended frost-free growing season, but may be detrimental in regions with short post-harvest, frost-free periods.