Delaying grapevine budbreak and/or phenological stages

Abstract

Context and purpose of the study – In the current climatic context, with milder winters leading to earlier budburst in most wine regions, vines are exposed to the risk of spring frosts for a longer period. Depending on the year, frost can lead to yield losses of between 20 and 100 %, jeopardizing the economic survival of wine estates. In addition, by destroying young shoots, spring frosts can impact the following season’s production, by reducing the number of canes available for pruning, for example. Late pruning is one method to combat spring frosts.

Material and methods – Experiments were conducted at Montpellier SupAgro-INRA campus (southern France; 43°38N, 3°53E) experimental vineyard. 20 year old Syrah grafted on SO4 were used for the experiment. The vines were Lyre trained and spur pruned. The vines were drip irrigated and fertigation was managed according to vine needs.  For the delayed pruning experiment, pruning was carried out by hand according to the grapevine physiological stage as opposed to calendar date.  Pre and post budbreak pruning were trialed. For pre budbreak pruning the following stages were considered: endodormancy, ecodormancy and the grapevine bleeding period. For post bud break cane pruning, the pruning dates were chosen according to the concept of acrotony on the winter cane and according to the phyllochron. Berry fresh mass and cane fresh mass and sugar concentration were analysed.

Results –
Pre-budburst: The most effective period for pruning to delay budburst is during the bleeding phase. Clearly, this raises the question of feasibility related to the size of vineyard to be pruned and the logistics in terms of labor. In this respect, mechanical pruning can be an advantage, with its speedier implementation allowing for late pruning.
Post-budburst : The pruning period will depend on the “grape variety × climate” interaction versus early or late grape varieties and cool or warm climate applying the concepts of acrotony, considering the phyllochron and the carbon reserves of the vine. Adjustment by wine region and by family of grape varieties is necessary, depending on how early budburst occurs for them. Recommendations are provided following on our study using Syrah as a model under Mediterranean climatic conditions.