Tolerance of Six Legumes to Common Turf Herbicides James D. McCurdy and J. Scott McElroy; Auburn University, Auburn, AL.

1. Results & Discussion • Only field foliar DW differed due to herbicide-by-species interaction effect. In general, herbicide effects were similar within legume species. However, results of trifloxysulfuron were somewhat unexpected. That is, trifloxysulfuron reduced T. arvense and T. repens DW < 34% and all other legumes ≥ 70% (Data not shown). • Herbicide main effect upon visual injury, DW, and height assessments generally concur. That is, bentazon, imazethapyr, MCPA, and 2,4-DB were acceptable in both field and greenhouse experiments (< 45% injury). Field visual injury was least due to imazethapyr, 2,4-DB, and bentazon (< 40%) while all other treatments injured legumes > 80%. Similarly, greenhouse visual injury was least due to imazethapyr, bentazon, and MCPA (< 40%) and greatest due to atrazine, dicamba, clopyralid, 2,4-D, and triclopyr (≥ 90%). • Species main effect upon visual injury and height reduction was significant. M. arabica was more susceptible to herbicide injury than all other plants in the greenhouse experiment (> 95% injury across all herbicides; Data not shown). With the exception of T. arvense, M. arabica height was reduced greater than that of other species in the greenhouse experiment (≥ 75%). In the field, M. arabica was more susceptible to herbicide injury (> 95%) than T. arvense, T repens, and T. incarnatum. M. arabica, T. arvense, and T. dubium heights were reduced > 65% across herbicide. Objective Field and greenhouse experiments evaluated cool-season legume response to common turf-herbicides. Ball Clover (TrifoliumnigrescensViv.) Tolerance of Six Legumes to Common Turf HerbicidesJames D. McCurdy and J. Scott McElroy; Auburn University, Auburn, AL. Materials and Methods Field experiments were arranged as randomized complete blocks on turf density (3 replicates) and were conducted during winters 2010 and 2011 at the Auburn University Turfgrass Research Unit (Auburn, AL) on a Marvyn sandy loam soil (fine-loamy, Kaolinitic, thermicTypicKanhapludult) with pH 6.3 (1:1 soil H2O-1). Legumes (Table 1) were collected 7.6 cm deep via golf-green cup-cutter and matured in a climate-controlled greenhouse prior to transplant into dormant bermudagrass (Cynodondactylon) turf as randomized sub-units within main plots. Main plot treatments included 12 common turfgrass herbicides and an untreated control for statistical comparison (Table 2). Herbicides were applied one month after transplant in 2010 and one week after transplant in 2011. In 2011, an analogous greenhouse experiment was conducted. The experiment was conducted as a completely random design within a climate-controlled greenhouse (22.8 and 25.6°C). Plants were handled similar to field experiments but were placed within loosely taped coffee-filters to prevent soil erosion from daily-applied over-head irrigation. Visual injury was assessed weekly relative to the control. Height and dry-weight (DW) were assessed 6 weeks after treatment (WAT) during 2011 only. Data were subject to analysis of variance within SAS® procedure GLIMMIX. Visual injury data were binomially distributed while height and weight data were normally distributed. Visual injury data did not differ due to year and were therefore combined. Interaction effects were considered significant at P ≤ 0.1000 while main effects were restricted to P ≤ 0.0500. Mean separation was performed via calculated confidence limits. Visual injury confidence limits are based upon adjusted inflation differences after back transformation and are therefore asymmetrical. Conclusions On a practical level, our results demonstrate selective herbicide options for maintaining biodiverse turf-legume swards. Candidate herbicides include bentazon, imazethapyr, MCPA, and 2,4-DB. Future Research • Our experiments failed to indicate varying herbicide tolerances between legume species. Differential herbicide tolerance of legume species (Young et al. 1992) and cultivars within species (Dear et al. 1995) has previously been reported. Therefore, future research must evaluate an even broader range of legumes and herbicides. • Thorough cost-benefit analysis must determine whether turf-legume swards are more sustainable than conventional grass-alone systems. Efforts are underway to estimate N-sharing with associated bermudagrass as well as soil- N and carbon flux due to mixed turf-legume swards. • Little is known about establishment and maintenance of mixed turf-legume swards. Ongoing research investigates establishment methods, seeding- rate and timing, as well as companion grass scenarios. Introduction The turfgrass industry is experiencing new demands for ecologically and economically -sustainable maintenance options. Additionally, government regulation of nutrient and pesticide -application necessitates the development of alternative turf systems. Inclusion of leguminous species that biologically fix nitrogen (N) is a proposed means of increasing the sustainability of certain turf scenarios. Nevertheless, weeds such as Digitaria,Cyperus, and Dichondraspecies continue to be problematic within biodiverse turf-legume swards. Herbicide options for maintaining turf-legume swards are limited. Due to the diverse range of legumes inhabiting turf, tolerance across a broad range of legumes must be investigated. Visual Injury (%) References Dear, B. S., G. A. Sandral, and N. E. Coombes. 1995. Differential tolerance of Trifolium subterraneumL. (subterranean clover) cultivars to broadleaf herbicides. 1. Herbage yield. Australian Journal of Experimental Agriculture 35, 467-474. Young, R. R., K. J. Morthorpe, P. H. Croft, H. Nicol. 1992. Differential tolerance of annual medics, Nungarin subterranean clover and hedge mustard to broadleaf herbicides. Australian Journal of Experimental Agriculture 32, 49-57. Relative Height Relative Weight White Clover (Trifoliumrepens L.) Rabbitfoot Clover (Trifoliumarvense L.) Small Hop Clover (TrifoliumdubiumSibth.) Special Thanks to Dr. Edzard van Santen, Michael Flessner, and Andrej Svyantek. @jamesdmccurdy www.auburnturf.com Spotted Bur Clover (Medicagoarabica (L.) Huds.) Crimson Clover (Trifoliumincarnatum L.)