EFFECT OF ADJUVANTS ON THE THERAPEUTIC ACTIVITY OF DIMETHOMORPH IN CONTROLLING VINE DOWNY MILDEW .2. ADJUVANT MIXTURES, OUTDOOR-HARDENED VINES AND ONE-PACK FORMULATIONS

Previous investigations have shown that certain C-12-C-18 alcohol etho xylates with between 5 and 20 moles ethylene oxide gave large enhancem ents to the therapeutic activity of emulsifiable concentrate (EC) and wettable power (WP) formulations of dimethomorph in controlling two-da y-old infections of downy mildew (Plasmopara viticola, Berl. & deT) on glasshouse propagated vines (Vitis vinifera, L.). In a continuation o f that work it has been shown that similar enhancements could also be obtained on vines that had been grown under outdoor conditions for two to three weeks before treatment (outdoor-hardened vines) and it is co ncluded that the treatments would therefore be effective on field vine s.Mixtures of either ammonium sulfate or the silicone ethoxylate, 'Sil wet' L77, with the best alcohol ethoxylates, 'Genapol' CO50 or 'Genapo l' CO80, produced slight antagonism of the action of the 'Genapols' an d therefore were of no benefit. Trials with one-pack formulations prep ared containing the 'Genapol' adjuvants produced good dose response cu rves from which estimated doses for 90% fungal control (ED(90) values) could be calculated by Logit analysis. These one-pack formulations we re significantly more effective than the standard EC formulation (ED(9 0) = 335 g AI ha(-1), glasshouse vines and 445 g AI ha(-1), outdoor ha rdened vines) with optimum enhancements with those formulations contai ning an adjuvant: dimethomorph ratio of either 9:1 on glasshouse vines (ED(90) = 13 g AI ha(-1)) or 6:1 on outdoor-hardened vines (ED(90) = 30 g AI ha(-1)). This last result was significantly better than that o btained with a commercial formulation of cymoxanil, 'Fytospore', (ED(9 0) = 86 g AI ha(-1)) and encouraged the recommendation that these one- pack formulations should be examined in field trials.