The release of methyl orange (MO) into bodies of water represents a serious environmental problem due to its chemical stability, toxicity, and persistence. To address this issue, this work presents the green synthesis of silver nanoparticles (AgNPs) using natural extracts of rose leaves (RL), rose petals of the pink Castile rose (PCR), and common yellow rose petals (YRP) as reducing agents. The formation of the AgNPs was confirmed by ultraviolet–visible (UV-Vis) spectroscopy through the localized surface plasmon resonance (LSPR) band and Transmission Electron Microscopy (TEM) obtaining sizes smaller than 15 nm, while FTIR analysis confirmed the presence of phenols, flavonoids, and proteins, which are suggested by spectral shifts to act as reducing and stabilizing agents. After optimizing the synthesis, the AgNPs were supported on gamma-alumina (γ-Al₂O₃). Gamma-alumina is characterized by a large surface area and high chemical and thermal stability; it inhibits nanoparticle agglomeration, thereby significantly improving electron-hole pair separation in photocatalytic processes, ultimately forming AgNPs/γ-Al₂O₃ photocatalysts. The activity of these composites was evaluated in the degradation of MO under UV irradiation (254 nm) and white light LED (380–750 nm). The catalysts demonstrated a dye removal trend, achieving degradation efficiencies under ultraviolet light of 4.94% (RL), 24.69% (YRP), and 60.49% (PCR); these figures increased under white LED light to 43.21% (RL), 64.20% (YRP), and 76.54% (PCR) after 60 min. It is hypothesized that this enhanced performance under visible light arises from mechanisms driven by reactive oxygen species (ROS) boosted by the LSPR effect, as has been documented in similar plasmonic systems. It is concluded that these supported photocatalysts constitute an environmentally friendly, sustainable, and alternative for wastewater treatment.