Washington Navel Orange

Effects of 2,4-D on the size of the navel-endopening and fruit quality of ‘Washington’ Navel orange

Large, protruding navel-end openings of navel oranges (Citrus sinensis (L.) Osbeck) are a major cull factor in the packhouse and make the control of some insects very difficult. Previous work on navel orange trees suggested that the synthetic auxin, 2,4-dichlorophenoxyacetic acid (2,4-D), applied at full bloom at 20 mg·L-1 reduced the diameter of the navel-end opening. In a preliminary study to verify these results under South African conditions, similar results were obtained when 2,4-D was applied at 25 mg·L-1 at petal drop on ‘Palmer’, ‘Robyn’ and ‘Lane Late’ navel orange trees. To determine the optimal timing and concentration of application without any detrimental effects on fruit quality, 2,4-D was applied at 15, 25 or 35 mg·L-1 at either full bloom or petal drop to ‘Washington’ navel orange trees in the following season.