To synthesize the CuO NPs, the extract was first prepared using a ratio of 1 g of yerba mate to 10 mL of distilled water (1:10) under constant stirring for 30 min at 70 °C. The extract was then centrifuged for 30 min at 5000 rpm, vacuum filtered, and refrigerated at 4 °C . The synthesis of CuO NPs was based on the methodology of Koteeswari et al. with few modifications. To this end, 40 mL of the yerba mate extract was mixed with 1, 1.5, and 2 g of Cu(NO3)2•3H2O under constant stirring for 2 h, varying the reaction temperature by 40, 60, and 80 °C. After the synthesis reaction, the next steps were centrifugation for 30 min at 5000 rpm, washing with distilled water to remove residual nitrates, and drying in an oven for 24 h at 60 °C. The material was then calcined at 400 °C for 2 h and characterized . The condition that had the highest conversion yield of CuO NPs was selected, and the produced CuO NPs were applied to lettuce and tomato seeds (Figure ).