Fungicidal activity and chemical constitution. Part XXI: The activity of substituted 1, 4‐naphthoquinones and quinoline‐5, 8‐diones against apple powdery mildew

Several series of alkyl‐substituted amino‐, bromo‐, chloro‐, fluoro‐ and hydroxy‐1, 4‐naphthoquinones, as well as some 6‐alkylaminoquinoline‐5, 8‐diones and 7‐alkyl‐6‐hydroxyquinoline‐5, 8‐diones were prepared and tested as protectant fungicides against apple powdery mildew (caused by Podosphaera leucotricha). While most of the compounds did not reduce infection when applied at 10−3M, several 3‐alkyl‐2‐bromo‐and 3‐alkyl‐2‐chloro‐1, naphthoquinones were found to have ED50 values below 50 × 10−5M.