A water-in-oil (w/o) or oil-in-water (o/w) emulsion composed of an oily phase including one or more oils of crude or refined vegetable origin, and at least one non-ionic and/or anionic emulsifying surfactant, and of an aqueous phase, the aqueous phase including at least one phyllosilicate, as a phytopharmaceutical adjuvant intended to be mixed with at least one phytopharmaceutical active agent or as a phytopharmaceutical product with mechanical action. A phytopharmaceutical composition including an active agent and also a phytopharmaceutical adjuvant as defined above, and a method of treating plants with the composition.