AbstractThe eradicant activities of 24 nitrogen‐containing preparations, comprising primary, secondary or tertiary amines, amine acetates, diamines, amine oxides or quaternary ammonium salts, were assessed in trials with potted dormant apple rootstocks, heavily infected with the powdery mildew fungusPodosphaera leucotricha.The surfactants consisted of mixtures in which C12/C14or C16/C18alkyl or alkenyl compounds predominated. Of the amine acetates (at 50g litre−1), only the formulation containing C12/C14primary amine acctates was considered worthy of further evaluation. Some amine oxides and quaternary ammonium compounds (at 35 g litre−1) were good eradicants and were as effective as ‘PP222’ a (nonylphenol‐ethoxylate mixture) which was included for comparison. All the compounds showing good activity contained one C12/C14alkyl group whereas C16/C18compounds, whether saturated or unsaturated, were relatively inactive. In a field trial, C12/C14(dimethyl) amine oxide, C12/C14bis (2‐hydroxyethyl) amine oxide, and C12/C14amine acetate (35 g litre−1) greatly reduced the amount of primary mildew on trees that were previously heavily infected, but there were signs that the fruit yi
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