Control of superficial scald on Granny Smith apples with diphenylamine

Abstract

The preliminary work of Smock (1955) indicated that treatment of apples with diphenylamine (DPA) offered a promising new method of controlling superficial scald on cool-stored apples. The effect of DPA and various methods of application hare been widely studied under Australian conditions over five seasons, Granny Smith apples grom-n in New South Wales being used. Treatment of fruit with a suitable concentration of DPA prevented the development of scald on fruit cool-stored in air, in controlled atmospheres, and in polyethylene film box liners, even when scald was severe and not controlled by oiled wraps. DPA was successfully applied to the fruit by impregnating it into standard paper wraps, by post-harvest dipping, and by pre-harvest spraying. It was found that there was a quantitative relation between the severity of scald and the concentration of DPA required to control it. DPA was shown to have a very limited mobility in the fruit. Residues in the fruit were related to both the amount applied and the method of application, and in all cases were low after cool storage. DPA appears to have a sufficiently low phytotoxicity for use as a pre-harvest spray. Its human toxicity is still under investigation. If approved for use on apples it will probably be in a purified form.