Herbicide tolerance of two cold-resistant bermudagrass (Cynodon spp.) cultivars determined by visual assessment and vehicle-mounted optical sensing

This study assessed the tolerance of 'Midlawn' (Cynodon dactylon X C. trans vaalensis) and 'OKS 91-11' (C. dactylon) bermudagrass to commonly used post emergence herbicides and compared visual assessment with vehicle-mounted op tical sensing (V-MOS) for evaluating herbicide phytotoxicity. Two postemerg ence herbicides were applied to mature stands of Midlawn and OKS 91-11 at t wo and four times label rates, and seven postemergence herbicides were appl ied at standard and two times label rates. Visual evaluation and spectral a ssessments were made for turf color 2, 7, 14, and 21 d after treatment (DAT ). Triclopyr and triclopyr plus clopyralid at 2X and 4X label rates caused significant damage on OKS 91-11 and Midlawn bermudagrass in both July and S eptember experiments. MSMA at 2X rate and MSMA + metribuzin at 1X and 2X ra te caused up to 73% color reductions that disappeared within 21 DAT in both cultivars. During July, 2,4-D plus mecoprop plus dicamba at the 2X rate ca used at least 18% injury to Midlawn bermudagrass for 21 d. Metribuzin was s afe at the 1X rate but caused significant injury for up to 7 d at the 2X ra te. Imazaquin and halosulfuron-methyl each caused significant damage on one rating date, Pronamide caused no change in color regardless of rate or tim e of application, OKS 91-11 tolerated 2x rates of 2,4-D plus mecoprop plus dicamba better than Midlawn, but cultivar responses to other herbicide trea tments were similar. V-MOS was effective for measuring green color reductio n on bermudagrass turf. V-MOS and visual evaluation were linearly related ( P < 0.01) at a strength of r = 0.58. Statistical results obtained using vis ual rating and V-MOS were the same in 86% of all cases.