Fungicidal activity and chemical constitution. XX. The activity of substituted 1,4‐naphthohydroquinone esters and substituted 1,4‐naphthoquinones against powdery mildews

Eleven 2‐n‐alkyl‐, ten 2‐n‐alkyl‐3‐hydroxy‐ and ten 2‐n‐alkyl‐2,3‐epoxy‐3‐hydro‐1,4‐naphthoquinones, together with eighteen 1,4‐naphthohydroquinone esters were tested as protectant fungicides against the apple and cucumber powdery mildews (caused by Podosphaera leucotricha and Sphaerotheca fuliginea respectively). In.general the former pathogen was more susceptible to compounds from all four series, the lowest 105ED50(M) being 0.7 for 2‐n‐octyl‐2,3‐epoxy‐3‐hydro‐1,4 naphthoquinone.