Herbicide effects on dormant and postdormant hybrid bermudagrass putting green turf

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 (T90) 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% (DOT30), depending on location. In two site-years characterized by increased abiotic stress, methiozolin applied at 1000 g ai ha-1 caused 44 DOT30. Cumyluron never injured hybrid bermudagrass over 30% or delayed T90 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.

Methiozolin rate and application frequency influence goosegrass (Eleusine indica) and smooth crabgrass (Digitaria ischaemum) control in turf

“…Bensulide plus oxadiazon was the only treatment that unacceptably injured creeping bentgrass at any location and had 24 DOT 20 (data not shown), which is consistent with previous reports of creeping bentgrass susceptibility to this herbicide combination (Johnson 1982, 1987). These results are also consistent with previous reports of hybrid bermudagrass tolerance to methiozolin when applied during periods of active growth at labeled rates (Peppers and Askew 2023) and with creeping bentgrass tolerance to methiozolin when treated in fall or spring (Askew and McNulty 2014; Brosnan et al 2013; Hoisington et al 2014).…”

“…preemergence for 4 wk when applied preemergence to bare ground (Koo and Hwang 2013). Methiozolin has a considerable margin of safety when used on creeping bentgrass putting greens (Askew and McNulty 2014;Brosnan et al 2013;Hoisington et al 2014), and recent reports suggest that the product can be safely used on actively growing hybrid bermudagrass putting greens (Peppers et al 2023). The relatively short persistence of methiozolin (Hwang et al 2013) suggests that low-dose, frequent application programs may be needed to maintain season-long weed control as has been shown with other herbicides (Brewer and Askew 2021).…”

Dissipation of spring-applied methiozolin in turfgrass systems

“…It is possible that the initial C. dactylon ×transvaalensis root regeneration had already occurred before the first treatment in 2022 based on these differences in green turf cover between years. Previous research has shown that C. dactylon × transvaalensis is more sensitive to methiozolin when treated just before post-dormancy green up compared with midtransition (Peppers and Askew 2023). New root production as C. dactylon × transvaalensis breaks dormancy may cause increased methiozolin absorption that would account for both the increased injury observed in previous studies and loss of methiozolin concentration in the current study.…”