Fungicidal control of rust of French prune caused by Tranzschelia discolor

Abstract

An orchard spray trial indicated that the dithiocarbamates mancozeb and zineb, the latter with or without the addition of white oil as a sticker, gave superior control of prune rust to dithianon, captafol or triforine. Further orchard studies involving artificial inoculation supported this result, with mancozeb and zineb giving 12-13 weeks of complete protection in one instance. In these studies chlorothalonil and bitertanol were also superior to dithianon and captafol, but appeared to be less persistent than the dithiocarbamates. Propiconazole and RH-3866 were relatively ineffective protectants.The efficacies and persistence of fungicides appeared to be less the later they were applied in spring and summer. Rain within a day or two of spraying appeared to reduce fungicide efficacy and persistence, but when it occurred some days or weeks later there was little effect, even a heavy fall (53 mm) not causing an observable reduction in efficacy. The implications of these findings for the development of control strategies is discussed.