Measuring chlorophyll fluorescence is a noninvasive, highly sensitive and fast way to give important information about the photosynthetic apparatus of plants. Applications of five doses (73.3, 110, 165, 247.5, 371.2 g ai ha-1) of the post emergent broad leaf herbicide Dicamba+2, 4-D were tested on greenhouse-grown wild mustard (Sinapis Arvensis). Results showed that herbicide application changed the shape of the chlorophyll fluorescence induction curve (Kautsky curve) two days after spraying (DAS). Fluorescence parameters such as Fv/Fm, maximum quantum efficiency of PS II and Fvj, variable fluorescence at the J step were significantly reduced at the recommended dose (371.2 g. ai. ha-1). Fvj was determined as a rather stable parameter compared to the Fv/Fm. At dose of 371.2 g. ai. ha-1, the Kautsky curves were almost turned to the straight lines, demonstrating serious damage to plant photosynthesis apparatus. These results demonstrate the possibility of measuring chlorophyll fluorescence as an easy, fast and cost effective method, to study the efficacy of auxin type herbicides.

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