Measurement of chlorophyll fluorescence in plants is an efficient tool for studying photosynthesis and can also be used to detect frost and heat stress in plants. As many herbicides affect photosynthetic processes, chlorophyll fluorescence offers higher sensitivity compared to that of, for instance, biotests based on inhibition of growth. Chlorophyll fluorescence analysis is a sensitive and early indicator of damage to photosynthetic apparatus. An experiment to study chlorophyll fluorescence as an indicator to detect herbicide stress in artichoke was conducted in 2008 in Giessen, Germany. Eight different post emergence herbicides (Phenmedipham, Pyridate, Quizalofop-P, Prosulfocarb, Carfentrazone, Rimsulfuron, Aclonifen and Clomazone) were used against a manually weeded control. Chlorophyll fluorescence data were recorded by Mini-PAM (WALZ) at 1 DAA, 1. 2, 3, and 4 WAA under direct sunlight and dark adapted conditions during two growth phases.

Chlorophyll fluorescence showed a very quick response to the applied herbicides and showed minimum values in Clomazone treated plots right after its application (1 DAA). This effect went on increasing and was followed by adverse effects of Aclonifen and Rimsulfuron, which showed their effect at 1 WAA. The adverse effect of all herbicides on chlorophyll fluorescence started decreasing from 3 WAA and it was near to normal (compared to control) at 4 WAA. Chlorophyll fluorescence data showed a full recovery of artichoke during the first growth phase and failed to do so in the second one. Failure of artichoke for complete recovery against the herbicide stress during second growth phase, 2008 may be a reason of the environmental factors like sunlight and air temperature. Artichoke flourishes well under bright and sunny days, which prevailed during the first growth phase of artichoke growth and the crop recovered against this stress. Contrarily, less sunshine and lower air temperature were observed during the second growth phase.