To evaluate the impact of the herbicide flumioxazin (fmx) on nontarget grapevines, its effects were assessed on fruiting cuttings and field-grown plants. The stress caused by the herbicide differed according to the grapevine model. In cuttings, leaf gas exchange and photosynthetic pigment levels as well as hexose contents decreased, whereas sucrose and starch accumulated, suggesting an inhibition of photosynthesis and an increase of carbohydrate reserves as a response to the fmx-induced stress. Paradoxically, in the field-grown grapevine leaves, fmx caused a stimulation of photosynthesis, an accumulation of photosynthetic pigments and monosaccharides, in parallel with a mobilization of sucrose and starch. These results suggest that fmx reaches grapevine leaves via root uptake and has prolonged effects. In cuttings, fmx generated a toxic effect related to its target, whereas in field-grown plants, fmx had rather positive physiological effects and acts as a signal further stimulating photosynthesis and related parameters.