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Early detection of crop injury due to off-target drift of herbicide is critical in crop production. Subtle changes in canopy reflectance could present useful information to detect the onset of crop stress. This study was conducted in a greenhouse to evaluate a portable spectroradiometer and a portable chlorophyll fluorometer for the detection of crop injury caused by glyphosate spray. In this study, several plants of a non-glyphosate resistant soybean (Glycine max) variety were subjected to spray from a pneumatic track sprayer operated in a spray chamber. Four plants received a rate of 0.86 kg ae/ha glyphosate and four plants received 0.086 kg ae/ha. Additional four non sprayed plants were used as controls. After the spray treatment, the chlorophyll reflectance of the plants was measured with the spectroradiometer at 4, 24, 48, and 72 hours to determine the plant response to herbicide. Simultaneously, with the reflectance measurement, the portable chlorophyll fluorometer was used to measure fluorescence induction kinetics of the crop under stress. Results of the study indicated that the plant chlorophyll reflectance measurement could provide useful information on crop stress 24 hours after treatment and that plant chlorophyll fluorescence measurement could provide information on crop stress 48 hours after the treatment.