Adjuvant Effects on the Therapeutic Control of Potato Late Blight by Dimethomorph Wettable Powder Formulations

Abstract

Dimethomorph is an effective Oomycete fungicide useful for the control of late blight (Phytophthora infestans, deB) on potatoes (Solanum tuberosum, L.) by preventative (prophylactic) sprays. The results of glasshouse trials using S. tuberosum plants inoculated one day prior to treatment showed that the weak to moderate curative (therapeutic) action of a wettable powder formulation of dimethomorph (WP1) could be substantially enhanced by spray tank adjuvants. A limited survey of surfactant adjuvants indicated that enhancements of performance of WP1 varied with the ethylene oxide content in two series of surfactants, C12/C14 alcohol ethoxylates (‘Genapol’ C series) and nonylphenol ethoxylates (‘Arkopal’ N series). Optimum enhancements were obtained with intermediate degrees of ethoxylation and ‘Genapol’ C080 was adjudged to be marginally superior to its analogues and superior to all of the ‘Arkopal’ series, as well as to a silicone ethoxylate/propoxylate (‘Silwet’ L-77), an alkylamine ethoxylate/propoxylate (‘Armoblen’ 557), and sodium sulfosuccinate (‘Aerosol’ OTB). It was also superior to an emulsifiable paraffinic/naphthenic oil (HVI 60E). Further trials established that relatively high application rates (1000–1500 g ha−1) of ‘Genapol’ C080 were required for maximum enhancement and that the presence of mancozeb, as a co-fungicide, did not substantially affect the enhancement of the therapeutic performance of dimethomorph by ‘Genapol’ C080.