On an industrial scale, the residues accumulated in essential oil distilleries can be compared to the volume of residues produced in a textile industry. Although these residues are discarded, they possess molecules with diverse biological activities, including their application in phytopathogen control. In this study, the chemical profile of the residue from the hydrodistillation of Lantana camara L. leaves was determined using High-Performance Liquid Chromatography (HPLC). Additionally, the effect of the residue on cells was assessed by determining plasma membrane integrity, levels of reactive oxygen species (ROS) production, and mitochondrial potential depolarization. The viability and cell density of Phytomonas serpens parasites significantly decreased after treatment with increasing concentrations of the lyophilized residue. RL038, the lyophilized residue from accession LAC-038, reduced cell viability by an average of 61.36%. ROS levels increased by approximately 2x and 3x at RL038 concentrations of 120 µg/mL and 180 µg/mL, respectively. It was observed that the same concentrations modified mitochondrial potential, reducing fluorescence by 44.6% and 46.8%, respectively. Analytical liquid chromatography of RL038 revealed the presence of 17 peaks subsequently classified as phenolic acids and flavonoids. RL038 from the hydrodistillation of Lantana camara L. leaves is a source of biologically active compounds with antiprotozoal potential.