Herbicide effects on dormant and post-dormant hybrid bermudagrass putting green turf

Abstract

Abstract Herbicide resistance coupled with a dearth of selective herbicide options has increased complexity of annual bluegrass control in hybrid bermudagrass putting greens. Cumyluron, endothall, and methiozolin are herbicides that have controlled annual bluegrass by inhibiting sites of action that are novel compared to herbicides currently used for turfgrass management in the US. However, peer-reviewed literature has no information on hybrid bermudagrass putting green tolerance to these herbicides. Sixteen field studies were established on eight golf greens in Midlothian, VA, in 2021 and 2022 to evaluate effects of cumyluron, endothall, methiozolin, pronamide and trifloxysulfuron on bermudagrass spring transition. The 16 studies were split equally between initiation during full dormancy versus mid-spring transition. Methiozolin applied at 500 and 1000 g ai ha -1 typically increased the heat units (growing degree days with a base temperature of 15 C) required for hybrid bermudagrass to visibly achieve 90% green coverage (T 90 ) when applied to fully dormant hybrid bermudagrass. This delay in green coverage was more pronounced at sites where hybrid bermudagrass vigor was seemingly reduced via abiotic stressors. Endothall was generally more injurious than all other treatments when applied to hybrid bermudagrass during mid-transition. Endothall applied at 840 g ai ha -1 injured hybrid bermudagrass for 0 to 9 d over a threshold of 30% (DOT 30 ), depending on location. In two site-years characterized by increased abiotic stress, methiozolin applied at 1000 g ai ha -1 caused 44 DOT 30 . Cumyluron never injured hybrid bermudagrass over 30% or delayed T 90 regardless of application timing. These results indicate methiozolin should only be applied within labeled rates to actively growing hybrid bermudagrass putting greens, cumyluron can be safely applied at 6450 g ai ha -1 on dormant or actively growing bermudagrass greens, and endothall applications should be limited to dormant bermudagrass greens unless transient phytotoxicity is acceptable.