Creeping bentgrass infestations in cool-season turfgrass are unsightly and difficult to control. Field tests were conducted at Stoney Creek Golf Course in Wintergreen, VA, in 2002 and 2003 on a Kentucky bluegrass rough and at the Turfgrass Research Center in Blacksburg, VA, in 2003 on a perennial ryegrass lawn to determine the efficacy of imazaquin, isoxaflutole, and mesotrione for creeping bentgrass control and turfgrass tolerance. Isoxaflutole and mesotrione each applied in two sequential applications at 280 g ai/ha or three sequential applications at 170 or 60 g/ha and imazaquin in two sequential applications at 390 g/ha controlled bentgrass at least 92% 14 wk after initial treatment (WAIT) at all locations. Sequential applications were applied at 2-wk intervals. Isoxaflutole and mesotrione, regardless of rate or sequential treatment, injured turfgrass less than 20% at all rating dates and locations. Imazaquin in two sequential applications at 390 g/ha injured Kentucky bluegrass and perennial ryegrass greater than 50% at all locations 14 WAIT. Results indicate isoxaflutole or mesotrione could be used for selective bentgrass control in Kentucky bluegrass or perennial ryegrass.

Turf managers traditionally avoid seeding cool-season turfgrass in spring due to summer annual weed interference and poor growing conditions for cool-season grasses. Siduron is the most accepted herbicide for weed control in spring-seeded tall fescue, but it has low residual activity and does not control many weeds other than crabgrass. Isoxaflutole, mesotrione, and quinclorac were evaluated as alternatives to siduron. Single applications of these herbicides controlled crabgrass equivalent to or better than siduron. Sequential applications of isoxaflutole, mesotrione, or quinclorac effectively controlled smooth crabgrass without injuring tall fescue. Isoxaflutole and mesotrione controlled broadleaf plantain, henbit, and yellow woodsorrel; quinclorac marginally controlled henbit; and siduron did not control broadleaf weeds. Turfgrass cover 9 wk after seeding was dependent on environment and equivalent between treatments except at a location with predominately broadleaf weeds where siduron treatments resulted in less cover due to weed infestation. Sequential applications of isoxaflutole, mesotrione, and quinclorac provide an effective, safe option for chemical weed control during establishment of cool-season turfgrass.

Isoxaflutole and mesotrione have been used to control creeping bentgrass in cool season turf, these experiments evaluate these two products for selective nimblewill control. Three experiments were conducted in Virginia and Tennessee to evaluate selective control options for nimblewill in cool-season turfgrass. Single applications of isoxaflutole control nimblewill more effectively than single applications of mesotrione. Nimblewill control 8 wk after initial treatment (WAIT) increased as mesotrione rates increased from 28 to 280 g ai/ha, and isoxaflutole rates increased from 28 to 168 g/ha. Isoxaflutole at 84 and 168 g/ha were the only single application treatments that controlled nimblewill greater than 80% 8 WAIT. However, sequential applications of isoxaflutole and mesotrione at 28 g/ha, 10 d apart controlled nimblewill 94 and 80%, respectively 8 WAIT. Triclopyr and fenoxaprop-p did not effectively control nimblewill and caused unacceptable turfgrass injury. Long-term control was not evaluated in these studies. However, it was concluded that isoxaflutole and mesotrione at appropriate rates and applied in sequence selectively control nimblewill without harming desirable turf.

Infestations of Italian ryegrass are difficult to control and decrease marketability of cool-season sod. Tests were conducted at three locations in Virginia in 2002 and 2003 to determine herbicide control options for Italian ryegrass in 90:10 tall fescue: Kentucky bluegrass turfgrass seeded the previous fall. Chlorsulfuron, diclofop, fluazifop plus fenoxaprop, and metsulfuron controlled 5- to 30-tiller Italian ryegrass less than 50% 10 wk after initial treatment (WAIT). Nicosulfuron at 53 g ai/ha controlled Italian ryegrass 69 to 95% and injured turf no greater than 10% at all locations 10 WAIT. Primisulfuron at 53 g ai/ha controlled Italian ryegrass less than 30% in 2002 and 59 to 63% at two locations in 2003 10 WAIT and injured turf less than 5% at all locations. Results indicate nicosulfuron can be used for Italian ryegrass control in tall fescue or tall fescue and Kentucky bluegrass turf if temporary injury is acceptable.

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 the adjacent creeping bentgrass. When evaluated 5, 10, and 25 d after treatment, visible track length and creeping bentgrass injury were greatly reduced by irrigating perennial ryegrass 2 h after treatment or by irrigating both perennial ryegrass and creeping bentgrass prior to simulated mowing. Visible injury of tracked turfgrass persisted for 36 d after treatment when irrigation was not applied and for as few as 5 d 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 the recovery of injured creeping bentgrass. Our results suggest that when applying rimsulfuron near susceptible bentgrass, the lowest effective rate should be applied and that the bentgrass should be irrigated at least 2 h after treatment to prevent nontarget injury.