Spontaneous N,N'-dibutylurea (DBU) formation in Benlate DF formulation under elevated temperatures.

Thermal degradation of benomyl in the fungicide Benlate DF at temperatures higher than 55 degrees C leads to the formation of N,N' -dibutylurea (DBU). External moisture is not required, since starch, an "inert" ingredient in the formulation, serves as a source of water. Enhanced phytotoxicity of the heat-treated, DBU-rich Benlate DF was demonstrated by lettuce seedling bioassay. Temperatures higher than 70 degrees C were recorded in a metal shipping container in June 1995 in Hawaii. Accumulation of DBU was observed in Benlate DF sealed in ampules and stored in this container. It is concluded that DBU formation is an intrinsic characteristic of Benlate DF at the temperatures tested. High temperature and high humidity in tropical regions provide ideal conditions for DBU formation in Benlate DF.