Photolysis, metabolism and other factors influencing the performance of triadimefon as a powdery mildew fungicide

Abstract

Abstract Triadimefon, 1‐(4‐chlorophenoxy)‐3,3‐dimethyl‐1‐( 1,2,4‐triazol‐1‐yl)butanone, applied at low dosage rates to leaves of marrow, apple or barley plants gave effective control of the appropriate powdery mildew fungi. The compound appeared to be systemic and to have considerable vapour‐phase activity. In marrow plants, up to 56% of triadimefon was metabolised to a mixture of two corresponding diastereoisomeric secondary alcohols. The mixture was identical with that obtained by chemical reduction of triadimefon. This mixture was also a very effective systemic fungicide and active in the vapour‐phase. Triadimefon was also reduced when incubated with Aspergillus niger but this was important only in shake culture. In replacement culture experiments, mycelial mats of this fungus converted the compound into a different metabolite, its isopropyl analogue. This may have resulted from participation of triadimefon in the C‐4 demethylation processes involved in fungal biosynthesis of ergosterol. Photolysis caused cleavage of the C‐1 to triazole bond liberating 1,2,4‐triazole, 4‐chlorophenol and 4‐chlorophenyl methyl carbonate, all of which were non‐fungitoxic. The importance of this photolysis in the in‐vivo situation is discussed.