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

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Abstract
When applied to Valencia orange trees at full bloom, aqueous sprays of 2,4-D 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. Young navel fruits sprayed at this time with concs. of 25-225 ppm. 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 ppm. of 2,4-D developed a thick rind and grew excessively large, protruding navels; other fruits became cylindrical. Fruit on Valencia orange trees treated in May with a conc. of 225 ppm. of 2,4-D developed a thick, pebbly rind. Other fruit on these trees became cylindrical and developed small navels. Applied to Valencia orange trees bearing mature fruit, the sprays decreased pre-harvest fruit-drop as much as 78%, even when applied 2 weeks after severe drop had begun.

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