Some Effects of 2,4-Dichlorophenoxyacetic Acid on Fruit-Drop and Morphology of Oranges

Some effects of aqueous sprays of 2,4-dichlorophenoxyacetic acid (2,4.-D) on fruit-drop and morphology of oranges are reported. 2. When applied to Valencia orange trees at full bloom, these sprays delayed blossom-drop 8-10 weeks, or more, but did not increase fruit-set. Applications in May likewise delayed the June drop of immature Washington Navel orange fruits 6-8 weeks but did not increase yield. 3. Young Navel fruits sprayed at this time with concentrations of 25-225 p.p.m, of 2,4-D developed seeds, or seedlike structures, in contrast to unsprayed fruits, which were seedless. Some fruit on the trees sprayed with concentrations of 225 p.p.m, of 2,4-D developed a thick rind and grew excessively large, protruding navels; other fruits became cylindrical in shape. 4. Fruit on Valencia orange trees treated in May with a concentration of 2.25 p.p.m, of 2,4-D developed a thick, pebbly rind. Other fruit on these trees became cylindrical in shape and developed small navels. 5. Applied to Valencia orange trees bearing mature fruit, the sprays decreased preharvest fruit-drop as much as 78%, even when applied 2 weeks after severe drop had begun. 6. Until additional data are available from studies now in progress, these sprays are not recommended for commercial use.