Research Note: Benefits and Drawbacks of Pre-bloom Applications of Gibberellic Acid (GA3) for Stem Elongation in Sauvignon blanc

Dense grape clusters have a high predisposition to bunch rot. An elongation of cluster stems could resultin a loosening of the cluster structure. To achieve such an elongation, gibberellic acid (GA3; 10 ppm)was applied to Sauvignon blanc either when three, five, seven, nine, 11 or 13 leaves were unfolded or atfull bloom in the 2010 season. In the present season, all applications led to stem elongation, a reductionof cluster compactness as well as a reduction of bunch rot severity. The density index proved to be anefficient tool to describe the predisposition of grape clusters to bunch rot. Best success was achieved if theapplication took place when seven leaves were unfolded. In the subsequent season (2011; the year followingthe year of application), the number of inflorescences per shoot, the length of the clusters, as well as theyield were considerably reduced, especially in the treatments with promising positive effects on the clusterstructure and disease severity. Hence, the present study shows the loosening potential as well as the riskof pre-bloom gibberellic acid applications. Due to the observed negative resultant effects, the pre-bloomapplication of GA3 at the present concentration (10 ppm) cannot yet be recommended for practical use inSauvignon blanc.