ZnO, Cu, and Cu2O/Cu nanoparticles (NPs) were evaluated for the degradation of methylene blue (MB) by three different approaches, namely, photocatalysis, Fenton-like, and photo-Fenton. Additionally, the in-vitro antifungal activity of the NPs was evaluated against three different phytopathogenic fungi, namely, Fusarium oxysporum, Fusarium solani, and Colletotrichum gloeosporioides. We found that the photo-Fenton degradation of MB was very similar for the three evaluated materials, with a degradation higher than 99.5%. On the other hand, the Cu2O/Cu-NPs was the best material for both the Fenton-like process and as an antifungal. Cu2O/Cu-NPs showed inhibition of radial growth as high as 96% for F. oxysporum, 74% for F. solani, 89% for C. gloeosporioides. Here we show that one nanomaterial could be effective for both degradation of dyes and pest control.