Factors affecting degradation rates of five triazole fungicides in two soil types: 1. Laboratory incubations

Triazole fungicides are now widely used commercially and several are known to be persistent in soil. The degradation rates of five such fungicides wer e measured in laboratory tests with two soils over 720 days, with analysis of soil extracts by high-pressure liquid chromatography. Behaviour in a san dy loam and a clay loam were similar, and incubation of the compounds eithe r singly or in admixture did not influence loss rates except for those of f lutriafol which were lower in the latter. Triadimefon was quite rapidly red uced to triadimenol, though traces of the former were always found, indicat ing a possible redox equilibrium. Flutriafol, epoxiconazole and triadimenol (derived from triadimefon) were very persistent, breakdown following first -order kinetics with half-lives greater than two years at 10 degrees C and 80% field capacity. Propiconazole was moderately persistent, with a half-li fe of about 200 days under these conditions. Degradation rates increased ab out 3-fold as the temperature was increased from 5 to 18 degrees C, though decreasing soil moisture to 60% field capacity only slightly slowed degrada tion. The rate constants obtained are used in a companion paper describing field studies on these two soils to compare laboratory-measured degradation rates with losses in the field following commercial sprays. (C) 1999 Socie ty of Chemical Industry.