Abstract

Background and goals Gibberellic acid (GA3) is sometimes used at prebl oom to hel p control cluster compactness, but controversy has been raised regarding its efficacy, particularly in table grape production. A trial was established to evaluate pre-bloom GA3 on rachis length. Methods and key findings In GA3-treated and untreated clusters, rachises were divided into three arbi-trary segments. The increase in length of each segment was evaluated from a month before bloom until the begin-ning of summer. Prebloom GA3 rapidly triggered rachis growth in length, but only in the middle and distal portions of the i nflorescence. The top area was not affected. The standard table grape cl uster ti ppi ng that fol l owed eliminated the cluster distal portion and all GA3 related rachis growth. GA3-treated clusters had longer segments removed compared to untreated ones. Shot berries and rachis thickness were also increased, but cluster and berry weight remained the same. Conclusions and significance The effects of GA3 on rachis l ength at prebl oom can be di scarded by other required standard table grape practices. The negative and cumula-ti ve effect s shoul d be consi dered when analyzing its usefulness. Know-i ng the benefits and disadvantages of this practice will help table grape grower s to opti mi ze pl ant growth regulator programs.