Methiozolin is applied five or more times per year to control annual bluegrass (Poa annua L.) in cool, temperate areas, but high market demand in the southern United States and recent registration in Australia has expanded the product’s use in variable climates. To better design weed control programs for variable turf types, more information is needed to characterize methiozolin dissipation in different turf systems. Methiozolin was applied biweekly three times to a Kentucky bluegrass (Poa pratensis L.) lawn and adjacent bare soil in New Jersey and on 12 hybrid bermudagrass [Cynodon dactylon (L.) Pers. × Cynodon transvaalensis Burtt Davy] putting greens in Virginia. Soil samples were collected immediately following each application and biweekly for 12 additional weeks. Methiozolin was extracted from each soil sample and analyzed using liquid chromatography with tandem mass spectrometry. Methiozolin was detected only within the top 2 cm of the soil (including verdure), but not below 2 cm, demonstrating its limited vertical mobility. Dissipation was significantly faster in turf-covered soil compared with bare soil. The time required for 50% methiozolin dissipation was 13 and 3.5 d in bare soil and turf-covered soil, respectively. In Virginia, methiozolin dissipation in the 1-m span of three sequential applications differed between years. Methiozolin concentration immediately following the third biweekly application to C. dactylon ×transvaalensis greens was approximately 105% and 180% of the concentration immediately following the initial application, in 2021 and 2022, respectively. This difference in methiozolin accumulation following three applications was attributed to differential C. dactylon ×transvaalensis green up during methiozolin treatments each year. Despite differences in posttreatment methiozolin concentration between years, the temporal dissipation rate later into the summer was consistent. Following the final application on C. dactylon ×transvaalensis greens, methiozolin dissipated 50% and 90% in 14 and 46 d, respectively. These data suggest that methiozolin dissipates more rapidly in turfgrass systems than in bare soil.

Herbicide resistance coupled with a dearth of selective herbicide options has increased the complexity of annual bluegrass control in hybrid bermudagrass putting greens. Cumyluron, endothall, and methiozolin are herbicides that control annual bluegrass by inhibiting novel sites of action compared with the herbicides currently used for turfgrass management in the United States. However, peer-reviewed literature contains 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 1,000 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 1,000 g ai ha−1 caused 44 DOT30. Cumyluron never injured hybrid bermudagrass by more than 30% or delayed T90 regardless of application timing. These results indicate that methiozolin should be applied only within labeled rates to actively growing hybrid bermudagrass putting greens, cumyluron can be safely applied at 6,450 g ai ha−1 to dormant or actively growing bermudagrass greens, and endothall applications should be limited to dormant bermudagrass greens unless transient phytotoxicity is acceptable.

Topramezone and carfentrazone + 2,4-D + mecoprop-p + dicamba (SpeedZone®) are herbicides labeled for POST goosegrass (Eleusine indica L. Gaertn.) control in hybrid bermudagrass (Cynodon dactylon × C. transvaalensis Burtt Davy). Field research was conducted in Knoxville, TN, during 2019 and 2020 to evaluate goosegrass control and hybrid bermudagrass tolerance to these herbicides applied alone and in mixture. Treatments included topramezone (12.2 g ha–1), SpeedZone® [carfentrazone (33.6 g ha–1) + 2,4-D (1,029 g ha–1) + mecoprop-p (322 g ha–1) + dicamba (91 g ha–1)] and SpeedZone® + topramezone at 12.2, 6.1, 3.6, or 2.4 g ha–1. A nontreated control was included for comparison. Hybrid bermudagrass tolerance was assessed on four cultivars (‘Northbridge’, ‘Tifway’, ‘Tahoma 31’, and ‘TifTuf’) via visual ratings of turfgrass injury and assessments of normalized difference vegetation index (NDVI). At the termination of the experiment, SpeedZone® alone and in mixture with topramezone controlled goosegrass better than or equal to topramezone alone. Mixtures of SpeedZone® + topramezone reduced injury on all cultivars compared to topramezone alone, particularly when mixtures delivered ≤6.1 g ha–1 topramezone. Injury subsided on all cultivars by 28 d after treatment regardless of herbicide. Findings suggest that SpeedZone® can be mixed with topramezone at the rates tested herein to minimize hybrid bermudagrass injury from topramezone applications for goosegrass control.

Several sulfonylurea herbicides are labeled for use on established bermudagrass or seashore paspalum, but label recommendations for many of these chemicals vary for sprigged turf. The objective of this study was to determine the safety of various sulfonylurea herbicides on newly planted, ‘Tifway’ bermudagrass and ‘Aloha’ seashore paspalum sprigs in Arkansas and Louisiana. Treatments were arranged as a five by two by two factorial with five herbicides (foramsulfuron at 29 and 59 g ai ha−1, halosulfuron at 35 and 70 g ai ha−1, metsulfuron at 21 and 42 g ai ha−1, sulfosulfuron at 66 and 131 g ai ha−1, and trifloxysulfuron at 28 and 56 g ai ha−1), two herbicide rates (low and high), and two application timings at 2 or 4 wk after sprigging (WAS). There was no discernable herbicide injury to, or reduction in, Tifway bermudagrass coverage in Arkansas, regardless of herbicide, application timing, or application rate. Trifloxysulfuron and metsulfuron were more injurious than other herbicides in Louisiana when applied at 2 WAS to Tifway bermudagrass, but injury levels were acceptable (< 15%), and there was no long-term reduction in establishment. Metsulfuron or halosulfuron applied at 2 or 4 WAS and sulfosulfuron applied at 4 WAS allowed > 90% establishment of Aloha seashore paspalum at both locations. Both trifloxysulfuron and foramsulfuron were injurious to seashore paspalum and reduced its establishment. These results suggest that sulfonylurea herbicides can be safely applied shortly after sprigging to Tifway bermudagrass and that metsulfuron, halosulfuron, and sulfosulfuron could be useful herbicides for establishing Aloha seashore paspalum from sprigs.

Annual bluegrass is a problematic weed in bermudagrass and other intensively maintained turfgrasses. Flumioxazin is reported to control annual bluegrass both PRE and POST; however, as a contact herbicide, flumioxazin injures actively growing bermudagrass. Research was conducted in Alabama and California to evaluate optimal flumioxazin application timing for annual bluegrass control, bermudagrass response, and overall sward quality in the field, and to assess annual bluegrass control at various growth stages in the greenhouse. November and December application timings resulted in the best balance of the three parameters. When bermudagrass was not dormant at application, treatment resulted in necrosis of green tissues and thus induced dormancy. The herbicide-induced dormancy resulted in better sward quality due to more uniform and therefore more aesthetically pleasing dormant turfgrass relative to natural dormancy. Flumioxazin at 0.43 kg ai ha−1 resulted in better annual bluegrass control and improved sward quality relative to 0.21 kg ha−1. Incomplete POST annual bluegrass control from later applications was attributed to larger weed size, limiting the effectiveness of this contact herbicide. Greenhouse data corroborated field results and indicated that flumioxazin at 0.43 kg ha−1 controlled ≥ 95% of annual bluegrass up to two tillers. Flumioxazin can be utilized for PRE and POST annual bluegrass control, but utilization of this herbicide is limited to dormant bermudagrass unless induced dormancy can be tolerated, and POST control is limited to annual bluegrass plants ≤ two tillers in size.

PRE herbicides have been reported to injure both the foliage and roots of hybrid bermudagrass turf established in sand culture. Research was conducted to evaluate the influence of reed-sedge peat moss (RSPM) on hybrid bermudagrass injury following PRE herbicide applications to plants established in sand culture. Washed sod plugs were established in mini-rhizotrons constructed with sand root-zones varying in organic carbon content (0.000, 0.003, 0.007, and 0.012 kg kg−1). Herbicide treatments included indaziflam (35 and 52.5 g ai ha−1) and prodiamine (840 g ai ha−1). Significant foliar injury was only observed with indaziflam at 52.5 g ha−1. When applied to plants in sand with no detectable (0.000 kg kg−1) organic carbon, foliar injury measured 61% by 6 wk after treatment. Comparatively, injury with indaziflam at 52.5 g ha−1 was reduced by 40% with applications to plants established in sand with 0.007 kg kg−1 organic carbon. Root length, root length density, and root surface area were greatest in sand-based root zones with ≥ 0.007 kg kg−1 organic carbon regardless of herbicide treatment; however, only indaziflam (52.5 g ha−1) and prodiamine-treated plants exhibited diminished root parameters relative to the nontreated check. Data in the current study illustrate that RSPM can affect above- and belowground injury following PRE herbicide applications to hybrid bermudagrass in sand root-zones.