Maintaining Peach Fruit Firmness and Quality

When plant growth regulators can make a difference

It is that time of the year when we finally have a marvelous surprise when visiting our preferred grocery store – Peaches are finally here and will be here for months!  There is a lot of management and preparation that goes in peach production to deliver to the stores a peach fruit with wonderful quality and aroma. Achieving and maintaining this quality is one of the most important goals in peach production from pre- to post-harvest decisions. The University of Georgia, in collaboration with the Georgia Peach producers, evaluated the use of plant growth regulators to maintain peach firmness and quality in 2014 and 2015. The results from these studies are presented in this article.

Traditionally, peach fruit is harvested using commercial standards that allow the peach producers to offer fruit that maintain firmness and quality during transport, delivery, and commercialization.  Peach growers generally have multiple varieties in their production inventory (approx. 30-40 different varieties in middle Georgia) allowing them to offer fresh peaches throughout their whole marketing season. Each variety can ripen in a period approximately of 1-2 weeks. However, sometimes there are production gaps that cannot be filled with the ripening window of the peach varieties currently available. There is great interest in extending the season of certain peach varieties to fill these gaps by both delaying fruit ripening on the tree and/or prolonging the storage life of the peaches. We at the University of Georgia Peach Team in collaboration with the Georgia Peach producers evaluated the use of plant growth regulators to maintain peach fruit firmness and quality in the tree by delaying fruit ripening in 2014 and 2015. The use of the growth regulators will allow peach growers to fill certain marketing gaps and maintain fruit quality.

Plant growth regulators have been used to improve growth, flowering, and fruit quality in different fruit crops. In peach, Valent BioSciences Corporation, IL has been offering two products, ProGibb® and Retain®, to improve peach fruit firmness and quality during harvest in the Southeastern US. ProGibb® is 4% gibberellic acid (GA3 – promotes growth and elongation of cells) liquid formulation and Retain® is 15% aminoethoxyvinylglycine (AVG – ethylene inhibitor) soluble powder formulation, both produced by fermentation.

Gibberellin has been reported to improve fruit quality, increase fruit size and firmness by delaying fruit maturity in peach (Dagar et al., 2012; Jackson, 1968; Ju et al., 1999; Olmstead and Futch, 2012; Zilkah et al., 1997). AVG is an inhibitor of ethylene synthesis, which is associated with fruit ripening and softening in peach. AVG has been reported to decrease fruit drop pre-harvest, delay fruit development, slow fruit softening, and increase firmness in peach (Byers, 1997; Ju et al., 1999; McGlasson et al., 2005; Olmstead and Futch, 2012; Rath and Wargo, 2004; Torrigiani et al., 2004).

In 2014 and 2015, the use of GA3 and AVG were evaluated in selected peach varieties. GA3 and AVG were applied with an airblast sprayer (333g/A of Retain® plus 20fl oz/A of ProGibb® 4% in a 100 gal/A spray volume, plus organosilicone surfactant). Applications were made two to three weeks before commercial harvest. Control plots were left untreated at the same locations for comparisons. Orchards were maintained following standard commercial management practices for the Southeastern US. Fruit was harvested from treated and untreated trees and fruit characteristics were taken for ‘Early August Prince’ and for ‘Ruston Red’ in 2014; and ‘Springprince’, ‘Juneprince’, and ‘Babygold’ in 2015. ‘Early August Prince’, ‘Ruston Red’ and ‘Juneprince’ are melting varieties. ‘Springprince’ and ‘Babygold’ are non-melting varieties.

Fruit was harvested from treated and untreated trees and fruit quality characteristics were taken. Single tree plots, a total of three to nine replications, were used for treated and untreated comparisons. Five fruit were harvested every three days starting approx. one week and ahalf before commercial harvest. Each fruit was rated individually. Fruit evaluations included rating the: blush, redness in the flesh, peach fuzz (1-9 scale), fruit tip (1-9 scale), firmness (1-9 scale, kgf, N), split pit, weight (g), and perimeter (mm). The subjective 1-9 scale represented values of 1 = undesirable to 9 = optimal. Blush and redness in flesh were rated as percent coverage. Split pit was rated as present or absent. Firmness was measured using a Wagner Model FT 30 fruit penetrometer (Figure 1).

In our study, we observed that the overall fruit characteristics, fuzz, tip, and split pit, showed no difference between treated and untreated for all the varieties across years. Percent blush, red flesh, perimeter, and weight for the treated and untreated did show some significant differences; however, these differences were not observed for most of the harvest dates. The fruit treated with plant growth regulators, GA3 and AVG, were firmer than the untreated fruit. In 2014, 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, but not for ‘Early August Prince’ in Pearson Farms. In 2015, differences in fruit firmness were seen in ‘Springprince’ and ‘Juneprince’ in the Fort Valley State University peach farm, and not for ‘Babygold’ in Fitzgerald farm (Figure 2).

The results from these trials were consistent with results from previous research of GA3 and AVG in peach. In this study, we observed variation in the effect of these plant growth regulators by varieties and locations. The evaluation of the fruit in this experiment was meant to determine the positive and negative effects of GA3 and AVG applications on fruit quality, primarily firmness.  It is necessary to study in the future the potential economic gain by using these products and the effect in the flowering vigor of the plant for the next season, as GA3 applications have been previously reported to affect return bloom in peach (Lurie and Crisosto, 2005). For additional results and information about this study please contact Dario Chavez at


Byers, D.H. 1997. Peach and nectarine fruit softening following aminoethoxyvinylglycine sprays and dips. HortScience 32:86-88.

Dagar, A., A. Weksler, H. Friedman, S. Lurie. 2012. Gibberellic acid (GA3) application at the end of pit ripening: Effect on ripening and storage of two harvests of ‘September Snow’ peach. Scientia Horticulturae, 140:125-130.

Jackson, D.I. 1968. Gibberellin and the growth of peach and apricot fruits. Austral. J. Biolog. Sci. 21:209-215.

Ju, Z., Y. Duan, Z. Ju. 1999. Combinations of GA3 and AVG delay fruit maturation, increase fruit size and improve storage life of `Feicheng’ peaches. J. Hort. Sci. Biotech. 74:579-583.

Lurie, S. and C.H. Crisosto. 2005. Chilling injury in peach and nectarine. Postharvest Biol. Technol. 37:195-208.

McGlasson, W.B., A.C. Rath, L. Legendre. 2005. Preharvest application of aminoethoxyvinylglycine (AVG) modifies harvest maturity and cold storage life of ‘Artic Snow’ nectarines. Postharvest Biol. Technol. 36:93-102.

Olmstead, M. and S. Futch. 2012. Using an ethylene inhibitor to increase fruit size, firmness, and storage quality in Florida peach production. Proc. Fla. State Hort. Soc. 125:13-16.

Rath, A.C. and J.M. Wargo. 2004. Aminoethoxyvinylglycine (AVG) applications to commercial blocs of ‘Tatura 204’, ‘Golden Queen’ and ‘Taylor Queen’ peaches delays fruit maturity and increases fruit size and quality. Acta Hort. 653:167-171.  

Torrigiani, P., A.M. Bregoli, V. Ziosi, S. Scaramagli, T. Ciriaci, A. Rasori, S. Biondi, G. Costa. 2004. Pre-harvest polyamine and aminoethoxyvinylglycine (AVG) applications modulate fruit ripening in Stark Red Gold nectarines (Prunus persica L. Batsch). Postharvest Biol. Technol. 33:293-308.

Zilkah, S., S. Lurie, R. Ben Arie, S. Antman, I. David, Y. Zuthi, Z. Lapsker. 1997. Preharvest sprays of gibberellin on ‘Flamekist’ nectarine trees to improve fruit storage potential. J. Hort. Sci. 72:355-362.

Figure 1. Peach fruit evaluation from green to commercially mature. Wagner Model FT 30 fruit penetrometer with the FT 516 tip. Photos by D.J. Chavez.

Figure 2. Fruit firmness (kgf) measured using a penetrometer in the GA3 and AVG trial for ‘Early August Prince’  in Lane Southern Orchards, Fort Valley, GA in 2014 (A), ‘Early August Prince’ in Pearson Farms, Marshallville, GA in 2014 (B), ‘Ruston Red’ in Lane Southern Orchards, Byron, GA in 2014 (C), ‘Springprince’ in Fort Valley State University peach orchard, Fort Valley, GA in 2015 (D), ‘Juneprince’ in Fort Valley State University peach orchard, Fort Valley, GA in 2015 (E), and ‘Babygold’ in Fitzgerald Farms, Woodbury, GA in 2015 (E). Green dotted line represents the date of commercial harvest. Red arrows represent dates with statistical significant differences between treated and untreated fruit.



Dario J. Chavez, Research and Extension Peach Specialist, Assistant Professor, Department of Horticulture, University of Georgia, Griffin, GA.

Jeff Cook, Georgia Peach Area Agent and County Extension Agent, Taylor and Peach Counties, University of Georgia, Fort Valley, GA.