In addition to their influence on the physicochemical properties and spray performance of formulations, the presence of adjuvants in the spray liquid can also influence the phytotoxic properties of the spray solution. The chemical composition of the surfactant plays a particularly important role. Fungitoxicity is influenced, as measured on three different fungi in vitro, but the interactions between active ingredient, adjuvant, and fungi are very specific. Possible relationships between biological activity and physicochemical properties are discussed.