Gibberellic Acid for Table Grape Inflorescence Elongation: Is It Worth It?

Background and goals Gibberellic acid (GA₃) is sometimes used at prebloom to help controlling cluster compactness, but controversy has been raised regarding its efficacy, particularly in table grape production. A trial was established to evaluate prebloom GA₃ on rachis length.

Methods and key findings In GA₃ treated and untreated clusters rachises were divided in three arbitrary segments. The increase in length of each segment was evaluated from a month before bloom until the beginning of summer. Prebloom GA₃ rapidly triggered rachis growth in length, but only in the middle and distal portions of the inflorescence. The top area was not affected. The following standard table grape cluster tipping 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 length at prebloom, can be discarded by other required standard table grapes practices. The negative and cumulative effects should be considered when analyzing its usefulness. Knowing the benefits and disadvantages of this practice will help table grape growers to optimize plant growth regulator programs.