Response of Tall Fescue Cultivars to Mesotrione Applied At Establishment.

Field studies were conducted in the fall of 2009 and 2010 in order to evaluate the response of eight newly seeded tall fescue cultivars to mesotrione applied at planting (PRE), and PRE followed by sequential treatment four weeks after turfgrass emergence (WAE) at rates ranging from 0.14 kg ai/ha to 1.125 kg ai/ha.  All applications were made with a single 9504EVS nozzle CO₂ pressured sprayer calibrated to deliver a total 178 L/ha at 222 kPa.  Experimental design is a strip plot (tall fescue cultivar x mesotrione application regime) with 4 replications.  Tall fescue cultivars ‘Rebel Advance,’  ‘Hounddog 5,’ ‘Bullseye,’ ‘3^rd Millenium,’ ‘Faith,’ ‘Falcon V,’ and ‘Mustang IV’ were seeded on 9 Sept 2009 and 30 Aug. 2010 at a rate of 295 kg/ha in 1.8 m wide rows using a drop spreader.  PRE application was made on 9 Sept. 2009 and 30 Aug. 2010 and PRE + 4 WAE on 6 Oct. 2009 and 10 Oct. 2010.  Tall fescue was visually evaluated for cover and injury in fall, as well as in the springtime on a scale of 0 (no cover or injury) to 100 (complete cover or injury).   In this study, reductions in establishment were visible for some of the cultivars at 1.125 kg ai/ha applied PRE or PRE + 4 WAE.  The most severe reductions occurred in the PRE + 4 WAE were visible in cultivars ‘Rebel Advance’ and ‘Hounddog.'  There is some degree of intraspecific variability, with cultivars ‘Bullseye,’ ‘3^rd Millenium,’ ‘Faith,’ and ‘Mustang IV’ showing the most tolerance to 1.125 kg ai/ha applied twice while ‘Rebel Advance’ and ‘Hounddog’ were more sensitive.  The results of this study suggest that although differences in tolerance to mesotrione was observed in some cultivars, these differences were minor, suggesting that tall fescue cultivars should all respond similarly to mesotrione applications.