Measurements of net photosynthesis, chlorophyll a fluorescence and solute leakage were evaluated as techniques for rapid detection of grass tolerance to fenoxaprop-ethyl and sethoxydim. Net photosynthesis measured as net CO2 uptake of the youngest fully expanded leaf of Calamagrostis arundinacea ‘Karl Foerster’ (Feather Reed Grass) detected tolerance to fenoxaprop-ethyl and susceptibility to sethoxydim 4 days after treatment and prior to the observation of visual injury. Sethoxydim reduced photosynthesis compared to untreated controls but fenoxaprop-ethyl did not. Measurements of older leaf (second most recently fully expanded leaf) photosynthesis were less consistent than those of the younger leaf. Chlorophyll a fluorescence of Calamagrostis leaf segments following treatment with fenoxaprop-ethyl and sethoxydim was ineffective for detecting grass tolerance. Solute leakage from leaf discs treated with 50 to 500 μg ml−1 fenoxaprop–ethyl and 10 to 100 μg ml−1 sethoxydim indicated differential tolerance of Calamagrostis and johnsongrass to fenoxaprop–ethyl and centipedegrass and johnsongrass to sethoxydim. Fenoxaprop–ethyl increased solute leakage from susceptible johnsongrass at 100 μg ml−1 while the 500 μg ml−1 concentration was required to cause substantial solute leakage from tolerant Calamagrostis. Sethoxydim caused greater leakage from johnsongrass than from centipedegrass at 50 and 100 μg ml−1. The best potential rapid screening technique was solute leakage measurements.