Abstract: A method and composition for fungicidal treatment of diseased trees such as those infected with Dutch elm disease or oak wilt involves the injection into the tree of a highly water soluble fungicide which is a blend of quaternary ammonium chloride compounds namely, dimethyl benzyl ammonium chloride, dimethyl ethylbenzyl ammonium chlorides and water. In strong concentrations, this composition is also usable as a sylvicide to kill trees for the purposes of clearing large sections of agricultural land in underdeveloped countries.