The effect of rainfall on copper spray residues on kiwifruit foliage fruit and canes

Abstract

Copper sprays are known to have protectant activity against the bacterial disease Pseudomonas syringae pv actinidiae (Psa) but their longevity on kiwifruit vines was unknown Commercial copper sprays were applied using a moving head tracksprayer to the fruit foliage and canes of Hayward kiwifruit after which simulated rain was applied in incremental amounts up to 100 mm The copper sprays were moderately resistant to rain washoff on leaves with at least 25 mm of rain required to remove 50 of the initial residues Copper sprays applied to both kiwifruit canes and fruit were highly resistant to rain washoff with up to 100 of the initial spray deposits still present after 50 mm of rain Up to four sequential copper sprays on fruit are unlikely to exceed maximum residue limits for fruit even in the absence of rain