Effects of Defoliation, Trellis Height, and Cropping Stress on the Cold Hardiness of Concord Grapevines

Abstract

The cold hardiness of bark and compound buds of culturally stressed Vitis labruscana Bailey 'Concord' grapevines was investigated in southwestern Michigan. Defoliation, pruning severity, and cluster thinning influenced cane and bud hardiness. The effect of trellis height on cane hardiness was inconclusive, though some increased hardiness was noted for low trellis buds. Complete defoliation by hand in August delayed acclimation in the fall and gave more rapid deacclimation in the spring. Effects of defoliation on cane and bud hardiness were more pronounced during the second year of treatment. Pruning severity was the most important factor influencing cane and bud hardiness in undefoliated plants. Field observations emphasized the importance to greater hardiness of balanced pruning at 30 + 10 severity as opposed to (60 + 10) pruning. Cluster thinning increased hardiness levels that had been depressed by 60 + 10 pruning, particularly when vines were defoliated. The greater sensitivity of underpruned vines seemed to be a result of the overproduction of fruit. With most treatments, the tertiary bud was as hardy as the secondary bud, or slightly hardier.