Late-Season Bermudagrass Control with Glyphosate, Fluazifop and Mesotrione Combinations for Spring Renovation.

Effective bermudagrass (Cynodon spp.) removal is necessary for proper spring cool-season turfgrass establishment. Common non-selective removal recommendations include multiple glyphosate applications while bermudagrass is actively growing.  Summer application timings are not practical for spring establishment of cool-season turfgrass. Experiments were initiated in 2013 in Manhattan, KS at Rocky Ford Research Center (RF) and Stagg Hill Golf Course (SH) to determine non-selective bermudagrass control with glyphosate, fluazifop and mesotrione combinations prior to winter dormancy for spring renovation. Research at RF and SH was conducted on hybrid ‘Midlawn’ bermudagrass [Cynodon dactylon (L.) Pers.× C. transvaalensis Burtt-Davy] and common  bermudagrass (Cynodon dactylon L. Pers), respectively. Turfgrass was maintained at 7.6 cm. Treatments were glyphosate (2.35 kg ha^-1), fluazifop (0.42 kg ha^-1) + NIS (0.25%v/v), mesotrione (0.28 kg ha^-1) + NIS, glyphosate (2.35 kg ha^-1) + fluazifop (0.42 kg ha^-1) + NIS, glyphosate (2.35 kg ha^-1) + mesotrione (0.28 kg ha^-1)  + NIS (0.25%v/v), fluazifop (0.42 kg ha^-1) + mesotrione (0.28 kg ha^-1) + NIS (0.25%V/V), glyphosate (2.35 kg ha^-1) + fluazifop (0.42 kg ha^-1) + mesotrione (0.28 kg ha^-1) + NIS (0.25%v/v), and a non-treated control for comparison. All treatments were applied 9 October 2013. Experimental design was a randomized complete block with four replications. Herbicides were applied to 1.5 x 1.5 m plots in 374 L ha^-1 water at 275 kPa with a CO₂ pressurized boom sprayer with XR8004VS flat-fan nozzles.  Collected data included visual percent green bermudagrass cover (0-100%) and Normalized Difference Vegetation Index (NDVI). Data was collected every 14 days after initiation (DAI) until bermudagrass resulted in 0% green cover (31 October 2013). Data collection resumed prior to spring green-up in May. Significant differences between RF and SH prevented pooling spring green-up data. No difference in bermudagrass green up was observed at RF. All treatments at RF resulted in 100% green bermudagrass cover by 25 August 2014. At SH non-treated, fluazifop, mesotrione, and fluazifop + mesotrione resulted in 100% green bermudagrass cover (25 August 2014). However, glyphosate, glyphosate + fluazifop, glyphosate + mesotrione, and glyphosate + fluazifop + mesotrione resulted in 38, 31, 19, and 34% green bermudagrass cover, respectively (25 Aug 2014). Research will be conducted the fall of 2014 to further examine differences between varieties.