Bispyribac-sodium selectively controls annual bluegrass in creeping bentgrass and perennial ryegrass, which might be attributed to differential metabolism among species. To test this hypothesis, we investigated metabolism of ¹⁴C-bispyribac-sodium in annual bluegrass, creeping bentgrass, and perennial ryegrass. Creeping bentgrass and perennial ryegrass metabolized approximately 50% of the ¹⁴C-bispyribac-sodium after 1 d, while annual bluegrass metabolized less than 20%. Parent herbicide recovered 7 d after treatment in annual bluegrass, creeping bentgrass, and perennial ryegrass was 73, 32, and 39% of total radioactivity per species, respectively. Polar metabolites recovered after 7 d in annual bluegrass, creeping bentgrass, and perennial ryegrass were 24, 59, and 55% of total radioactivity per species, respectively. Half-life of ¹⁴C-bispyribac-sodium in annual bluegrass, creeping bentgrass, and perennial ryegrass was estimated at greater than 7 d, 1 d, and 2 d, respectively. Results support the hypothesis that differential tolerances of these grasses are attributed to herbicide metabolism.

Nomenclature: Bispyribac-sodium; annual bluegrass, Poa annua L.; creeping bentgrass, Agrostis stolonifera L., ‘L-93’; perennial ryegrass, Lolium perenne L., ‘Manhattan 4’.