Herbicide Resistance in Annual Bluegrass on Tennessee Golf Courses

Research was conducted to determine the extent of herbicide resistance in annual bluegrass (Poa annua L.) randomly collected from Tennessee golf courses during 2018. Harvested plants were cultured for seed collection, with progeny screened for resistance to glyphosate (Roundup Pro; 32 fl oz acre(-1)), foramsulfuron (Revolver; 17.4 fl oz acre(-1)), simazine (Princep 4FL; 2 qt acre(-1)), or prodiamine (Barricade 65WG; 0.001 mM). In postemergence herbicide screens, annual bluegrass collections were grouped based on survival percentage: resistant (>30% survival), segregating for resistance (5-30% survival), or susceptible (<5% survival). For prodiamine, annual bluegrass collections were screened in hydroponics and deemed resistant when <20% of plants exhibited symptoms of herbicide treatment (e.g., club roots), whereas those with >90% of plants showing symptoms were deemed susceptible; the remainder were intermediate and classified as segregating for resistance. In total, 64% of the annual bluegrass collections had some degree of resistance to glyphosate. Similarly, 21% had some degree of resistance to foramsulfuron, while 58% of annual bluegrass collections had some degree of resistance to prodiamine. Only 3% of the annual bluegrass collections were susceptible to simazine, and 25% of those surviving treatment were resistant to glyphosate or foramsulfuron. Multiple resistance to glyphosate, foramsulfuron, and simazine was reported in 4% of the annual bluegrass collections. The results of this research highlight the need for more diversified weed management strategies to control annual bluegrass on Tennessee golf courses.