Differential Metabolism of Trifloxysulfuron In Sensitive Tall Fescue and Tolerant Bermudagrass Turf.

Trifloxysulfuron (Monument^TM) is a sulfonylurea herbicide that provides selective postemergence control of certain weeds and cool-season grasses in warm-season turf.  The objective of this study was to determine the role of metabolism as a basis for differential herbicide selectivity in sensitive tall fescue (Festuca arundinacea Schreb.) and tolerant hybrid bermudagrass (Cynodon dactylon (L.) Pers. x C. transvaalensis Burtt-Davy) ‘Tifway 419’ turf.  A preliminary experiment was conducted to refine analytical methods for sample preparation, extraction, separation, and identification of the parent compound and metabolites using a Waters Acquity Tandem Quadrapole mass spectrometer (MS-MS) coupled to UltraPerformance Liquid chromatography (UPLC). Fifty mg of young leaf tissue from each species was cut into small pieces and immersed into 100 ppm of analytical grade trifloxysulfuron in Petri dishes for 18 h under incandescent light. Ultraviolet absorbance (250 nm) and positive ion (m/z 460) MS revealed that, in tolerant bermudagrass leaves, about one-half of the absorbed parent compound had metabolized into two byproducts of equal concentration and greater polarity. However, in sensitive tall fescue, trace quantities of the parent compound and no metabolites were recovered in the leaf tissue. Analyses of the treatment solution/leaf wash for both species as well as a control without leaf tissue revealed the presence of the parent compound only. It appeared that the tall fescue leaves in this experiment absorbed little or no trifloxysulfuron. Subsequent experiments will involve analysis and identification of the parent compound and its metabolites in whole plant tissues of both species at 4 to 96 h after treatment with the commercial formulation of the herbicide.