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Fluorescence photography was used to evaluate the effects of bentazon, an herbicide that inhibits electron transport in photosystem II, on sunflower, taken as a model plant. We measured chlorophyll fluorescence to visualize the penetration, distribution, and effect of the herbicide on the plant. Our results showed that bentazon penetrates the leaf within 10–16 min, reaching full depth within 40 min. Also, we show that the herbicide is distributed along the conducting tissues of the leaf. The presence of necrotic spots, as well as the size of increased-fluorescence areas, were positively correlated to the concentration of herbicide. These findings suggest that fluorescence imaging may be a useful tool for observing the absorption and distribution of photosystem II-inhibiting herbicides in plants as an alternative to radioactive labeling in some cases.