A plant protection agent includes a photocatalyst particle including a titanium oxide compound. The surface of the photocatalyst particle is modified with a metal compound that includes a metal atom and a hydrocarbon group. The photocatalyst particle has absorption at a wavelength of 550 nm. The change in the absorbance of the photocatalyst particle at the wavelength of 550 nm which occurs when the photocatalyst particle is irradiated with white light having an illuminance of 3000 lux for 24 hours is 10% or more.
