Enhanced degradation of iprodione in soil after repeated treatments for controlling Sclerotinia minor

Poor field control of lettuce collar rot by iprodione was observed in southern France and was attributed to enhanced biodegradation of the fungicide. Enhanced biodegradation was obtained in vitro after repeated applications of iprodione to non-degrading soils. Normal soils became biodegrading after mixing with degrading soils (3 vol./1 vol.). Activity of the responsible microflora seemed dependent on soil physico-chemical characteristics.