investigation of the effects of clodinafop and dicamba+2, 4-d on kautskey curve and chlorophyll fluorescence

measurement of chlorophyll fluorescence is noninvasive, highly sensitive, fast and easy way to give important information about the photosynthetic apparatus. chlorophyll fluorescence parameters and kautsky curves of wild oat and wild mustard sprayed by clodinafop and dicamba+2, 4-d respectively was investigated at two green house experiments. the results indicated significant reduction at trend of fv/fm، fvj and area parameters five days after clodinafop spraying. the shapes of the kautsky curves were affected by clodinafop five days after spraying. the maximum fluorescence (fm) reduced significantly at 5 days after spraying. chlorophyll fluorescence parameters revealed clodinafop efficiency one week before herbicide symptoms occurred. chlorophyll fluorescence could be an alternative method to study herbicide efficacy compare to the classical method (measuring dry or fresh weight). at wild mustard the shape of the kautsky curve at higher doses of dicamba+2, 4-d (371.2 and 165.1 g ai./ha) was affected one day after spray. the kautsky curve quenching after 1000 ms did not occur two days after spray at the recommended dose (371.2 g ai./ha) but its decay was observed at under recommended doses at both one and two days after spray. finally although clodinafop and dicamba+2, 4-d are not directly psii inhibitor but they could change the kautsky curves shape and form before revealing visual symptoms of these herbicides.