Persistence to rainwashing of DDT wettable powders

The amounts of DDT removed by ‘rainwashing’ deposits of wettable powders on glass or cotton leaf surfaces were greatly diminished if the powders were formulated with amine stearates. The age and the density of the deposit affected retention to a lesser degree. Rates of loss by ‘rainwashing’ the deposits from both types of surface could be described in general terms by double exponential equations. The initial rate at which DDT penetrated into cotton leaves, but not the amount that penetrated after several weeks in the laboratory at 20°c, was influenced by the presence of amine stearates in the formulation (which formed stearic acid in the deposits). The proportional amounts, and the total amounts, of DDT that penetrated from these unweathered deposits depended on the deposit density.