Effect of Adjuvants on the Therapeutic Activity of Dimethomorph in Controlling Vine Downy Mildew. I. Survey of Adjuvant Types

Abstract

The effect of adjuvants on the performance of emulsifiable concentrate (EC) and wettable powder (WP) formulations of dimethomorph, a new systemic Oomycete fungicide, has been investigated using a two-day therapeutic (curative) assay with downy mildew (Plasrnopara uiricola, Berl. & de T.) on vines (Vitis uinifera L., cv. Cabernet Sauvignon) in glasshouse trials.The EC formulation had some therapeutic activity in this type of test. This activity was increased by the spray tank incorporation of 6 g litre-' of either emulsifiable rape seed oil ('Atplus' 412) or emulsifiable paraffinic oil ('Atplus' 41 1F). However, these improvements in performance were overshadowed by those brought about by incorporation of 3 g litre-' of a series of C,,/C,, alcohol ethoxylates varying in ethylene oxide content from 5 to 20 moles: ('Marlipal' 34/6E0, 34/11EO, 34/20E0). Nearly complete fungal control was obtained in the presence of these adjuvants with a dimethomorph application rate of 25 g ha-' compared with only around 90% control at 400 g ha-' without adjuvants.The WP formulation was inactive in this therapeutic test but the presence of the adjuvants improved the performance of this formulation towards the high levels observed with the EC plus adjuvants, demonstrating that adjuvants could markedly influence the performance of solid, otherwise therapeutically inactive, dimethomorph formulations.Further trials examined other types of adjuvants (nonylphenol, alkylamine and silicone ethoxylates) but either they were no better than the alcohol ethoxylates or they induced unacceptable phytotoxicity. Trials with alcohol ethoxylates ('Genapols') from another source demonstrated activity equivalent to the 'Marlipal' surfactants. A two-factorial matrix experiment with 'Genapol' C050 showed that, under glasshouse conditions, >90% control could be obtained with the dimethomorph EC at 25 g A1 ha-' with 375 g ha-' 'Genapol' COSO. Applications of the WP formulation required slightly higher rates of either 50 g A1 haplus 375 g ha-' 'Genapol' C050 or 25 g A1 ha-' plus 750-1500 g ha-' 'Genapol' C050.The overall conclusion was that alcohol ethoxylates varying in alkyl chain length from C,, to C,, and ethylene oxide content between 5 and 20 moles for the C,, surfactants and -15 moles for the C,, surfactants were effective adjuvants in promoting the therapeutic activity of dimethomorph formulations against P . uiticola on glasshouse-propagated vines.

Suspension Concentrate crop protection formulation design and performance for low spray volume and UAS spray application

“…[45][46][47] When formulated as micron sized particles, the foliar uptake of active ingredient is particularly low relative to solubilised active ingredient and adjuvants can be important to enhance leaf uptake in such formulation systems. 48,49 While few of these studies have investigated the effect of low spray volumes, Grayson et al in greenhouse studies investigated spray volume effects at 150 to 600 L/ha on easy and hard to wet crops with variable effects that were often the combined effect of several factors including the spray pattern, spray deposition, run-off and foliar uptake illustrating the importance of minimising combinations of factors. 50 These studies however did not explore effects at lower spray volumes.…”

“…There are several studies reporting the benefit of penetration enhancers on the biodelivery enhancement of poorly soluble, crystalline, lipophilic active ingredients and the reader is directed towards these for further information 45–47 . When formulated as micron sized particles, the foliar uptake of active ingredient is particularly low relative to solubilised active ingredient and adjuvants can be important to enhance leaf uptake in such formulation systems 48,49 . While few of these studies have investigated the effect of low spray volumes, Grayson et al .…”