The invention concerns a system (1) for characterising the physiological state of woody plants (2, 3) with branches grown in rows, such as vine plants, said system (1) including a vehicle (10) designed to move between said rows, a geolocation device (14) and a processing unit (15), and being characterized in that it includes a sensor (16) including a light source (17) designed to emit a light beam (18) and a light receiver (19), said light beam (18) being able to intersect the branches, as the vehicle (10) moves forward, said light beam (18) having a dimension (L) greater than the diameter (D) of the thickest of the branches in said row (6), said light beam (18) projecting, onto said light receiver (19), a shadow (20A, 208) from which the processing unit (15) determines the diameter (D1, D2 of the branch (2A, 28) in question.
