RAPID ONSET OF THE ACCELERATED DEGRADATION OF DICARBOXIMIDE FUNGICIDES IN A UK SOIL WITH A LONG HISTORY OF AGROCHEMICAL EXCLUSION

In field and laboratory experiments, enhanced degradation of the dicar boximide fungicides, iprodione and vinclozolin, was stimulated by only one application of the fungicides in a soil with no previous history of any pesticide input. Field and laboratory studies demonstrated the ease of stimulation by pretreatment with even very low concentrations of the fungicides (0.5 mu g g(-1) soil) and at a range of temperatures and soil moisture conditions. Soils that had acquired full enhanced d egradation could rapidly degrade fungicide applied at 30 times the rec ommended field rate. Cross-enhancement of degradation was noted with b oth fungicides, but not with their common metabolite, 3,5-dichloroanil ine. Application of the antibiotics chloramphenicol or rifampicin to s oil reduced enhanced degradation to control levels; cycloheximide had no effect. This, together with the inhibitory action of azide, mercuri c chloride and repetitive microwaving, indicated that the agent(s) of enhanced degradation was probably bacterial.