The persistence of gibberellin A 3 on plant surfaces was examined using fruit of `Marsh' seedless grapefruit (Citrus paradisi Macf.) and an inert glass model system . 14 Cgibberellin A, was applied to surfaces in aqueous treatment solutions or in waxing solutions . Dried-out treatment residues were removed by washing and analyzed for total and GA3 like radioactivity . Gibberellin A 3 persisted without significant loss for at least 7 d in aqueous treatment solutions (pH 4 .0 or 6 .2) but was less persistent in the pH 10.4 waxing solution (t 1 /2 = 7 d) .
Loss of total peel surface radioactivity was fast during the first 3 days, slowing down afterwards . After 14 days 73% of the initial radioactivity could still be recovered from fruit peel surface and 70% of the recovered radioactivity was still in the form of gibberellin A 3 . Gibberellin A, was somewhat more persistent in residues from pH 4 than pH 7 treatment solutions . Light had a slight enhancing effect on gibberellin A, decomposition on fruit peel under growth chamber conditions . After l2 d at 100% relative humidity, 88% of the radioactivity on glass surfaces was still in the form of gibberellin A 3 , as against 45% at a relative humidity of 50% . Simulated field conditions, combining daily fluctuations in light, temperature and relative humidity, markedly enhanced gibberellin A, decomposition on glass surfaces (t 1 /2 = 2 d) . Gibberellin A 3 was very persistent (90% after 9 d) in the waxing residues on fruit peel surface .