Methods for controlling a plant detection system include determining a target phase delay based on a first phase delay of reflected portions of a first light beam and a second phase delay of reflected portions of a second light beam. A composite light beam comprising the first light beam and the second light beam is emitter towards bare soil, and reflected portions of the composite light beam are detected. An intensity of at least one of the first light beam or the second light beam is adjusted so that a phase delay of the composite light beam is approximately equal to the target phase delay.