Comparison of foliar fertilizers and growth regulators on pre-harvest drop and fruit quality of ‘Thompson Navel’ orange

An investigation was carried out to determine the ability of foliar fertilizers and growth regulators to prevent pre-harvest drop and enhance navel orange fruit quality. Fifteen year old trees of the Thompson Navel orange variety were sprayed with aqueous solutions of one of the following: methanol (0.13%), calcium nitrate (0.25%), zinc sulfate (1%) + urea (0.5%), fermented sugar- cane extract (2.8%), salicylic acid (1 or 3 mM), citric acid (5 mM), or 2,4-dichlorophenoxyacetic acid (2,4-D) (0.002%). Results indicated that foliar treatment with 2,4-D reduced fruit drop (2.6%) as compared to the control (15.2%). Fruit decay was delayed and flavor improved by 5 mM citric acid. Weight loss was reduced after 3mM salicylic acid applica- tion, while methanol (0.13%), salicylic acid (1 and 3 mM) and citric acid (5 mM) caused a delay in fruit coloring.