Tolerance of 'Tifton 85', 'Jiggs', and 'Coastal' bermudagrass (Cynodon dactylon) to postemergence herbicides

Abstract

Field studies conducted in the summer of 1995 and greenhouse studies in the fall of 1995 and the spring of 1996 evaluated the response of 'Coastal', 'Jiggs', and 'Tifton 85' bermudagrass varieties to applications of postemergence herbicides. Treatments evaluated included picloram + 2,4-D at 0.35 and 0.71 kg ha-', dicamba + 2,4-D at 0.54 and 1.08 kg ha-', 2,4-D at 0.53 and 1.06 kg ha-', metsulfuron at 0.004 and 0.008 kg ha-1', triasulfuron at 0.01 5 and 0.03 kg ha-, picloram at 0. 14 kg ha-', dicamba at 0.56 kg ha-', and glyphosate applied at 0.56 kg ha-1'. Crop phytotoxicity in the field was measured by recording visual injury, plant length/density, and forage production. Phytotoxicity was evaluated on greenhouse grown plants by comparing dry matter forage weights. In the 'Coastal' variety moderate injury was observed from applications of glyphosate in the fall greenhouse study. Metsulfuron exhibited deleterious effects in the 1996 greenhouse studies. Positive effects were observed following the application of picloram + 2,4-D, 2,4-D, and dicamba in the field. Similar results were noted from 2,4-D, metsulfuron, triasulfuron, and dicamba treatments in the 1995 greenhouse study, and by 2,4-D in 1996 greenhouse studies. Comparable results were observed from glyphosate application in the 'Jiggs' variety. In the 1995 greenhouse study, deleterious effects were observed from applications of picloram + 2,4-D, dicamba + 2,4-D, metsulfuron, picloram, dicamba, and glyphosate. In the 1996 greenhouse study, only picloram and metsulfuron treatments exhibited injury to the 'Jiggs' variety. Glyphosate, when applied to the 'Tifton' variety caused significant injury at all application timings in the field and greenhouse. Triasulfuron at 0.03 kg ha-' also exhibited injury to the 'Tifton 85'variety in the field. Applications of picloram + 2,4-D and dicamba both increased forage production when compared to an untreated check. In the fall greenhouse study, picloram + 2,4-D, picloram, and glyphosate, caused injury to 'Tifton' while the dicamba application increased forage production. In the 1996 greenhouse study, picloram + 2,4-D, metsulfuron, triasulfuron, picloram, dicamba and glyphosate all decreased forage production compared to the untreated areas.