A Rapid Diagnostic Assay for Detecting Herbicide Resistance in Annual Bluegrass.

Reports of herbicide resistance in annual bluegrass (Poa annua L.) are greater than any other weed species commonly found in turf. Traditional means of testing annual bluegrass phenotypes for herbicide resistance are labor intensive, costly, and time consuming. Rapid diagnostic tests have been developed to confirm herbicide resistance in weeds of agronomic cropping systems that correlate well with traditional whole plant bioassays. Research was conducted at the University of Tennessee in 2016 to determine if agar-based rapid diagnostic tests could be used to confirm herbicide resistance in annual bluegrass phenotypes harvested from golf course turf. Separate experiments were conducted using annual bluegrass phenotypes resistant to acetolactate synthase (ALS) inhibiting herbicides and glyphosate via target site mutation; an herbicide susceptible control was included in each for comparison. Single tiller plants were washed free of soil and transplanted into autoclavable polycarbonate plant culture boxes filled with 65 mL of murashigee-skoog media amended with glyphosate (0, 6, 12, 25, 50, 100, 200, or 400 μM) or trifloxysulfuron (6.25, 12.5, 25, 50, 75, 100, or 150 μM). Treatments were arranged in a completely randomized design with 50 replications and repeated in time. Mortality in agar was assessed 7 to 12 days after treatment (depending on herbicide) and compared to responses observed after treating 98 individual plants of each biotype with glyphosate (560 g ha^-1) or trifloxysulfuron (27.8 g ha^-1) in an enclosed spray chamber. Fisher’s exact test (α = 0.05) determined that mortality in agar with 100 μM glyphosate was not significantly different than treating whole plants via traditional spray application. Similarly, mortality in agar with 12.5 μM trifloxysulfuron was not significantly different than spraying whole plants with herbicide. Our findings indicate that rapid diagnostic tests can reliably provide an assessment of annual bluegrass susceptibility to glyphosate or trifloxysulfuron in as few as 12 days or less.