A plant detection system includes a radiation module and a photodetector system. The photodetector system includes a photodetector housing, one or more photodetectors, a detector lens, and an aperture plate. The aperture plate is disposed within the photodetector housing between the detector lens and the one or more photodetectors and has an aperture extending therethrough. The detector lens and the aperture plate are configured so that stray radiation received by the detector lens is directed through the aperture in the aperture plate or onto a surface of the aperture plate without being directed onto sidewalls of the photodetector housing.
