Disclosed are various embodiments for a mobile rig configured to control a photoperiodic response of a photoperiodically sensitive plant subject (e.g., a short-day plant) planted in an open field. The mobile rig includes a support structure； wheels； and light sources attached to the support structure at a position for emitting light on an upper surface of the photoperiodically sensitive plant subject. The mobile rig includes or is coupled to a control circuit having processing circuitry configured to cause the mobile rig to navigate across an open field having the photoperiodically sensitive plant subject planted therein and selectively illuminate the photoperiodically sensitive plant subject using the light sources attached to the mobile rig, for instance, during nighttime hours in a wavelength range between approximately 250 nm and approximately 800 nm to control the photoperiodic response of the photoperiodically sensitive plant subject planted therein.
