Environmental context. Recent developments in environmental monitoring have revealed that pesticides are dispersed through all parts of the environment. Air, water and soil are all contaminated. In this context there are tightening regulations on pesticide use with the goal of limiting their environmental impact. We look here at how pesticides can actually break down very quickly after their application on leaves, due to the effect of sunlight, i.e. ‘photodegradation’. Understanding this phenomenon could help to reduce application rates.

Abstract. The fate of sulcotrione (a pesticide and herbicide) has been monitored on maize leaves after spraying. One hour after spraying, 10% of the active ingredient is already transformed by the action of solar light. Sulcotrione mainly undergoes photocyclisation. The photoproduct, which has been fully characterised, is easily detected on the leaf surface. The day after spraying, 90% of the sulcotrione initially detected has disappeared. Twenty three percent is detected as the cyclisation product. Two days after spraying sulcotrione is no longer detected but the photoproduct still represents 7% of the initial amount detected. This study brings out the importance of the photodegradation pathway after crop spraying.