AbstractThe control of powdery mildew on marrows (caused bySphaerotheca fuliginea) achieved with 4‐(1‐substituted alkyl)‐2,6‐dinitrophenols, 2‐(1‐substituted alkyl)‐4,6‐dinitrophenols, 4‐(1‐substituted alkyl)‐2,6‐dinitrophenyl crotonates, cycloalkyldinitrophenols, 2‐cyclohexyl‐halogeno‐nitrophenols and 4‐cyclohexyl‐2‐substituted‐6‐nitrophenols is discussed. Certain combinations of partition and intra‐ and intermolecular hydrogen bonding capacities lead to vapour phase and/or zonal activity or to penetration of the leaf surface followed by possible translocation, phytotoxicity or translaminar activity. The capacity of the phenol to hydrogen bond to the leaf cuticular waxes has a considerable influence upon the fate of these
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