Cultural Practices to Improve Primary Bud Cold Hardiness of Vidal Blanc Grapevines in the Continental Climate

Grapes grown in Kentucky face challenges including bud injury due to frequent occurrence of late spring frosts and critical minima and fluctuating winter temperatures.  Previously we demonstrated that yield components and cold hardiness were influenced by the severity of pruning and cluster thinning and cluster thinning alone defined the differences in leaf area: fruit ratio, vine size, and vigor.  The current study investigates the effects of delayed pruning, cluster number and bud position on primary bud survival of field-grown Vidal blanc grapevines at three commercial vineyards in central Kentucky.  Treatments were established in a randomized complete block design and all treatment vines were pruned to 20 +10 and shoot thinned to 3-5 shoots /m of row.    Vines were subjected to delayed and early season pruning and either one cluster per shoot or no cluster thinning.  Delayed pruning and increased crop level resulted in a decrease in primary bud cold hardiness and overall fruit quality compared to early season pruning.  Primary bud survival was dependent on bud position where positions 1-4 were 60% more tolerant to freezing temperatures than bud positions 5-8.   This data corroborates with our previous data suggesting that cluster thinning is the key component to maintaining vine sustainability of Vidal blanc with implications that bud position may impact primary bud hardiness.