Eradication of over-wintering mildew (Podosphaera leucotricha) in apple buds by nitrogen-containing surfactants

The 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 fungus Podosphaera leucotricha. The surfactants consisted of mixtures in which C12/C14 or C16/C18 alkyl or alkenyl compounds predominated. Of the amine acetates (at 50g litre−1), only the formulation containing C12/C14 primary 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/C14 alkyl group whereas C16/C18 compounds, whether saturated or unsaturated, were relatively inactive. In a field trial, C12/C14 (dimethyl) amine oxide, C12/C14bis (2‐hydroxyethyl) amine oxide, and C12/C14 amine 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 yield was reduced.