The changes in the photosynthetic activity of young plants (Clearfield hybrid PRIMIS) grown in pot experiments were studied, after both independent and combined treatment with the herbicide imazamox (120 ml/da) and suspension fertilizer Lactofol B (300 ml/da). In the imazamox-treated sunflower plants a slight yellowing of the younger leaves was observed, which was absent in the plants treated with the mixture of imazamox and Lactofol B. The photosynthetic activity in the plants treated with the mixture, measured by the leaf gas exchange parameters, the chlorophyll fluorescence and the amount of photosynthetic pigments were higher than in the imazamox-treated plants. The recovery of the photosynthetic activity in the plants treated with the herbicide was carried out faster after treatment with Lactofol B. The results showed the suspension fertilizer Lactofol B to have a preventive and remedial effect against treated with imazamox herbicide sunflower plants.