2,4-D residues in stored lemons from post-harvest treatments

Abstract

Lemons were treated under simulated commercial conditions with various forms of 2,4- dichlorophenoxyacetic acid (2,4-D) to reduce losses in storage from stem end rot caused by the fungus Diaporthe citri. The 2,4-D was applied either as a single packing line treatment in wax, or as a double treatment in a benomyl fungicide bulk dip followed by the packing line treatment. The fruit were held under commercially used storage conditions and analysed at intervals for 2,4-D residues. In one trial, the sodium salt at 100 to 500 mg 2,4-Dl-1 in wax was used, and the wax applied by the foaming and dipping methods, Initial residue levels on the fruit varied with rate of application of the salt, but foaming and dipping modes of application gave similar levels. At eight weeks, residues were only detectable in double treated fruit. In a second trial, the sodium and dimethylamine salts and the ethyl ester forms were used, as a single treatment at 500 mg 2,4-D l-1 in wax foam or a double treatment at 500 mg 2,4-D l-1 in a benomyl dip followed by 500 mg 2,4-D l-1 in wax foam. The residue levels were in the order: sodium salt < dimethylamine salt < ethyl ester. Residues declined in storage, but were still detectable after 12 weeks, except for the single treatment with the sodium salt. Residues from both single and double 2,4-D treatments were always within Australian and U.S permissible limits. Provided that the recommended rate of 500 mg 2.4-D l-1 is not exceeded, none of the 2,4-D formulations tested should give excessive residues in fruit.