In order to develop a new method for measuring foliar uptake of fungicides,
Congo Red was selected as a tracer, and optimum procedures were establishe
d for washing, extracting and analyzing it and fungicides from leaf surface
s. Congo Red, a water-soluble dye, was not absorbed into cucumber or rice l
eaf, even in the presence of various surfactants, and was completely washab
le from leaf surfaces by aqueous acetonitrile solutions. Congo Red and fung
icides in washings were quantified to calculate the amount of foliar uptake
of the latter, by comparing the ratio to Congo Red. The optimum concentrat
ion of Congo Red in a formulation should be established in order to minimiz
e its influence on fungicide uptake. Although Congo Red has proved to be us
eful with a conventional droplet application method, it will give more real
istic and practical results with the spraying method used in the present st
udy. (C) 2001 Society of Chemical Industry.