The Effect of Gibberellic Acid (GA3) and Aminoethoyxvinylglycine (AVG) on Late-season Peach [Prunus persica (L.) Batsch] Varieties in Middle Georgia

The peach ripening season in middle Georgia spans 5 months beginning in the middle of May and concluding in the middle of September. Approximately, 60 different peach varieties are currently being grown in Georgia and ripen throughout this market season in which each variety is available for 1 to 2 weeks. Within the season, there are time points when variety ripening times may not overlap thus producing several days in which no fruit is available. This is clearly a problem in peach production in middle Georgia for certain late-season varieties. Plant growth regulators (PGRs) are widely used in apples, cherries, and other fruits. Gibberellic acid (GA3) and aminoethoyxvinylglycine (AVG) treatments in stone fruit have shown to increase fruit firmness, inhibit/decrease ethylene production, delay maturity and shift harvest windows, and reduce fruit drop. The objective of this research was to study the effect of GA3 and AVG on delaying maturity, increasing fruit firmness, and shifting the ripening window of two late-season ripening varieties. Plant growth regulators were applied with an airblast sprayer [333g/A of Retain® (AVG) and 20fl oz/A of ProGibb® 4% (GA3) in a 100 gal/A spray volume, plus organosilicone surfactant] on two late-ripening varieties: ‘Ruston Red’ in Lane Southern Orchards, Byron, GA; and ‘Early August Prince’ in Pearson Farms, Marshallville, GA, and in Lane Southern Orchards, Fort Valley, GA. Applications were made on early-mid June 2014, approximately 3 to 4 weeks before fruit harvest. Control plots were left untreated at the same locations for comparisons. A total of three replications, single tree plots, were used for treated and untreated comparisons. Fruit was harvested from treated and untreated trees and fruit characteristics were taken at approximately 2 to 3 weeks before commercial harvest. The effect of locations (Lane Southern Orchards and Pearson Farms) and varieties (‘Early August Prince’ and ‘Ruston Red’) were found to be statistically different (P<0.05).  Differences in fruit firmness were seen for ‘Early August Prince’ and ‘Ruston Red’ in Lane Southern Orchards for almost all plots after the first commercial harvest. ‘Early August Prince’ firmness in Pearson Farms did not show significant differences among treated and untreated fruit. The fruit treated with plant growth regulators, ProGibb® and Retain®, were firmer than the untreated fruit. This trial produced important and encouraging results; however, they were not consistent across varieties and locations. Additional trials could provide support for the use of these plant growth regulators.