Tolerance of Buffalograss to Glyphosate Herbicide Formulations and Rates During Winter Dormancy.

Glyphosate is commonly used for winter post-emergence weed control in bermudagrass and buffalograss, although current labels do not list recommendations for use on buffalograss during winter dormancy. ‘Bison’, ‘Texoka’, ‘Cody’, ‘Bowie’, ‘KDMW2006-15’ and a lawn comprised of multiple genotypes of local provenance were screened during winter dormancy for tolerance to an isopropylamine and a potassium salt formulation of glyphosate. Research was conducted at Stillwater, OK during late winter/early spring of both 2010 and 2011. Herbicide rates evaluated were 0.39, 0.58 0.77 and 1.54 pounds acid equivalent per acre. Carrier rate was 40 gallons per acre. Prior to treatment, 10 randomly selected areas of each stand measuring 929 square cm, were examined for the number of stems (vertical or horizontal) having visible green, red or purple colored leaves or internode segments. Viewing was conducted with the evaluator’s eyes at 61 cm directly above the top of the turfgrass canopy. Canopies were left undisturbed. Extremely dense canopies of dead buffalograss leaves were present in both years just prior to application on the Texoka, Cody, Bowie and KDMW2006-16 with no live tissue visible. No delay in greenup or decrease in turf quality was found due to glyphosate application in either year on these stands. Due to the management program and site usage, the Bison and native common buffalograss stands had very thin canopies which allowed substantial numbers of green, red or purple stems to be visible just prior to application in both years. Slight delays in greenup and occasionally reduced quality were found in the Bison and common buffalograss stands, however both stands recovered quickly and fully by mid spring in both years. Glyphosate rates traditionally used on bermudagrass appear appropriate on the buffalograss cultivars tested, provided that a dense canopy of dead leaves and stems are present to intercept spray droplets.