Abstract
The objective of this experiment was to determine the optimal time to apply gibberellic acid (GA) for increasing juice yield and improving peel quality of 'Hamlin' sweet orange (Citrus sinensis [L.] Osb.). Mature trees on sour orange ( Citrus aurantium L.) rootstock were sprayed with about 4 gallons of a solution of GA (18 g a.i./acre) and organo-silicone surfactant (Silwet, 0.05%) per tree. Trees were sprayed on either 26 Aug., 9 Sept., 2 Oct. (color break) or 13 Oct. 1997, or non-sprayed (control). Peel puncture force (PPF), peel color, and juice yield were evaluated monthly between December 1997 and March 1998. Fruit from trees sprayed with GA had peels with higher PPR and less yellow color than non-sprayed fruit at most harvest dates. The effect of GA on PPR and peel color persisted about 5 months after spraying. Juice yield was usually numerically greater for GA-treated fruits than for non-treated fruit. Fruit treated with GA at color break also had statistically greater juice yield when harvested by 24 Feb. than fruit from nonsprayed trees. Thus, GA applied at or near color break appears to be the most effective time for enhancing peel quality and juice yield of 'Hamlin' oranges. However, the effect of GA on juice weight was not consistent and did not persist past the normal 'Hamlin' harvest season.
