Recent advances in genetic engineering have led to the development of glyphosate-resistant (GR) crops for genetic markers and selective weed control. The effects of glyphosate residue on turfgrass clippings could be toxic to non-GR species. The objective of this experiment was to determine whether glyphosate would retain activity within clippings of creeping bentgrass when applied to Kentucky bluegrass and perennial ryegrass. Greenhouse-grown ‘Penncross’ and GR ‘ASR-368’ were treated with glyphosate at 2.24 kg/ha. Clippings were collected 1, 3, 7, and 12 d after application and applied to greenhouse-grown Kentucky bluegrass and perennial ryegrass. Kentucky bluegrass and perennial ryegrass dry weight and percent cover were reduced by clippings receiving glyphosate that were harvested 1 and 3 d after glyphosate application from both susceptible and resistant creeping bentgrass. Results indicate that glyphosate remains active in clippings for up to 3 d after treatment within creeping bentgrass clippings. Glyphosate-applied creeping bentgrass clippings will need to be managed to prevent injury to susceptible species.

Nomenclature: Glyphosate; creeping bentgrass, Agrostis stolonifera L.; Kentucky bluegrass, Poa pratensis L.; perennial ryegrass, Lolium perenne L.

Additional index words: Clippings, glyphosate, mulch, turfgrass.

Abbreviations: DAT, days after treatment; GR, glyphosate resistant; GRCB-G, glyphosate-resistant creeping bentgrass treated with glyphosate; PCB-G, Penncross creeping bentgrass treated with glyphosate; PCB-UTC, Penncross creeping bentgrass untreated control; UTC, untreated control.