ADJUVANT EFFECTS ON THE THERAPEUTIC CONTROL OF POTATO LATE BLIGHT BY DIMETHOMORPH WETTABLE POWDER FORMULATIONS

Dimethomorph is an effective Oomycete fungicide useful for the control of late blight (Phytophthora infestans, deB) on potatoes (Solanum tub erosum, L.) by preventative (prophylactic) sprays. The results of glas shouse trials using S. tuberosum plants inoculated one day prior to tr eatment showed that the weak to moderate curative (therapeutic) action of a wettable powder formulation of dimethomorph (WP1) could be subst antially enhanced by spray tank adjuvants. A limited survey of surfact ant adjuvants indicated that enhancements of performance of WP1 varied with the ethylene oxide content in two series of surfactants, C-12/C- 14 alcohol ethoxylates ('Genapol' C series) and nonylphenol ethoxylate s ('Arkopal' N series). Optimum enhancements were obtained with interm ediate degrees of ethoxylation and 'Genapol' C080 was adjudged to be m arginally superior to its analogues and superior to all of the 'Arkopa l' series, as well as to a silicone ethoxylate/propoxylate ('Silwet' L -77), an alkylamine ethoxylate/propoxylate ('Armoblen' 557), and sodiu m sulfosuccinate ('Aerosol' OTB). It was also superior to an emulsifia ble paraffinic/naphthenic oil (HVI 60E). Further trials established th at 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 enhancem ent of the therapeutic performance of dimethomorph by 'Genapol' C080.