Herbicide Tolerance of Two Cold-Resistant Bermudagrass (Cynodonspp.) Cultivars Determined by Visual Assessment and Vehicle-Mounted Optical Sensing1

Abstract

This study assessed the tolerance of ‘Midlawn’ (Cynodon dactylon × C. transvaalensis) and ‘OKS 91-11’ (C. dactylon) bermudagrass to commonly used postemergence herbicides and compared visual assessment with vehicle-mounted optical sensing (V-MOS) for evaluating herbicide phytotoxicity. Two postemergence herbicides were applied to mature stands of Midlawn and OKS 91-11 at two and four times label rates, and seven postemergence herbicides were applied at standard and two times label rates. Visual evaluation and spectral assessments were made for turf color 2, 7, 14, and 21 d after treatment (DAT). Triclopyr and triclopyr plus clopyralid at 2× and 4× label rates caused significant damage on OKS 91-11 and Midlawn bermudagrass in both July and September experiments. MSMA at 2× rate and MSMA metribuzin at 1× and 2× rate 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 2× rate caused at least 18% injury to Midlawn bermudagrass for 21 d. Metribuzin was safe at the 1× rate but caused significant injury for up to 7 d at the 2× rate. Imazaquin and halosulfuron-methyl each caused significant damage on one rating date. Pronamide caused no change in color regardless of rate or time of application. OKS 91-11 tolerated 2× rates of 2,4-D plus mecoprop plus dicamba better than Midlawn, but cultivar responses to other herbicide treatments were similar. V-MOS was effective for measuring green color reduction 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 visual rating and V-MOS were the same in 86% of all cases.Nomenclature: 2,4-D; bentazon; dicamba; halosulfuron-methyl; imazaquin; mecoprop; metribuzin; MSMA; prodiamine; pronamide; triclopyr; common bermudagrass, Cynodon dactylon (L.) Pers. OKS 91-11; hybrid bermudagrass, Cynodon dactylon (L.) Pers. × C. transvaalensis Burtt-Davy, Midlawn.Additional index words: NDVI, phytotoxicity, postemergence herbicide, spectral acquisition, turfgrass injury, turfgrass quality, variable-rate technology.Abbreviations: CA, commercially available; DAT, days after treatment; NDVI, normalized difference vegetative index; NIR, near infrared; OSU, Oklahoma State University; R, red; V-MOS, vehicle-mounted optical sensing.