Techniques for Detecting Grass Tolerance to Sethoxydim and Fenoxaprop-Ethyl Herbicides

Abstract

Measurements of net photosynthesis, chlorophyllafluorescence and solute leakage were evaluated as techniques for rapid detection of grass tolerance to fenoxaprop-ethyl and sethoxydim. Net photosynthesis measured as net CO2uptake of the youngest fully expanded leaf ofCalamagrostis 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. Chlorophyllafluorescence ofCalamagrostisleaf 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−1fenoxaprop–ethyl and 10 to 100 μg ml−1sethoxydim indicated differential tolerance ofCalamagrostisand johnsongrass to fenoxaprop–ethyl and centipedegrass and johnsongrass to sethoxydim. Fenoxaprop–ethyl increased solute leakage from susceptible johnsongrass at 100 μg ml−1while the 500 μg ml−1concentration was required to cause substantial solute leakage from tolerantCalamagrostis. 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.