Concern has been raised that herbicides often used to control perennial ryegrass in warm-season turf could move laterally or “track” and injure neighboring cool-season grasses.  Rimsulfuron was applied at 17.5 or 35 g ai/ha to perennial ryegrass in the afternoon.  The following morning while dew was still present, a greens mower was driven through the perennial ryegrass and across adjacent creeping bentgrass.  When evaluated 5, 10, and 25 days after treatment, visible track length and creeping bentgrass injury were greatly reduced by irrigating perennial ryegrass two hours after treatment or irrigating both perennial ryegrass and creeping bentgrass prior to simulated mowing.  Visible injury of tracked turfgrass persisted for 36 days after treatment when irrigation was not applied, and as few as 5 days when both perennial ryegrass and creeping bentgrass were irrigated.  Irrigation had no effect on perennial ryegrass control.  Gibberellic acid at 0.12 kg ai/ha and foliar iron at 1.3 kg ai/ha, applied when tracks first appeared, did not improve recovery of injured creeping bentgrass.  Results suggest that when applying rimsulfuron near susceptible bentgrass, one should apply the lowest effective rate, and irrigate at least two hours after treatment to prevent nontarget injury.

Nomenclature: Rimsulfuron; perennial ryegrass, Lolium perenne L. ‘Pennant II’; creeping bentgrass, Agrostis stolonifera L. ‘Penncross.’

Additional index words:  Dislodged pesticide; foliar iron; gibberellic acid; herbicide movement; tracking.

Abbreviations:  DATR, d after tracking;  E Spring, Early spring, May 30, 2003, Turfgrass Research Center, Blacksburg, VA 2003;  Fall, Fall, Oct. 2, 2002, Turfgrass Research Center, Blacksburg, VA; Gibberellic acid, gibberellic acid applied at 0.12 kg ai/ha;  Iron, foliar iron applied at 1.3 kg ai/ha;  L Spring, Late Spring, June 9, 2003, Turfgrass Research Center, Blacksburg, VA 2003.