Preliminary Results with the use of 2,4-Dichlorophenoxy-Acetic Acid as a Spray-Oil Amendment

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Abstract
Exploratory tests indicated that the addition of 0.025% 2,4-dichlorophenoxyacetic acid to undiluted spray oil applied to branches of either Washington Navel or Valencia orange trees strikingly decreased leaf and fruit drop, in comparison with trees similarly sprayed, but without 2,4-D. In preliminary field trials the addition of 0.025-0.05% 2,4-D to the oil in oil-water emulsion sprays (oil 12/3%) for use on orange trees significantly decreased leaf drop 26.5% to 57.4% compared with trees similarly treated but without 2,4-D. The % reduction depended on the properties of the oil and on the conc. of 2,4-D. In the one trial where fruit counts were possible, addition of 0.0037% 2,4-D to the spray oil significantly decreased fruit drop 30.9%, compared with drop from trees similarly sprayed, but without 2,4-D. The stage of bud expansion appears to be an important factor in the use of 2,4-D as a spray-oil amendment. At the present time 2,4-D as a spray-oil amendment cannot be recommended for commercial orchard practice, since under certain conditions not yet fully established injury to trees may result from its use.

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