Postemergence Control of Virginia Buttonweed with Metsulfuron Tank-Mixtures.

Virginia buttonweed (Diodia virginiana) is a difficult to control broadleaf perennial weed. Field experiments were conducted at Pine Hills Golf Club in Winder, GA to examine the control of Virginia buttonweed in a ‘Tifway 419’ hybrid bermudagrass fairway. The soil was an Appling sandy loam (Fine, kaolinitic, thermic Typic Kanhapludult). Research was conducted on a mature mature hybrid bermudagrass fairway maintained at a 1 cm height. Virginia buttonweed cover (25 to 35%) within each plot was determined at the time of initial herbicide application. Treatments were applied to plots (1.2 m x 1.5 m) arranged in a randomized complete block design with four replications. Treatments included a non-treated check, metsulfuron (0.021 kg ai ha^-1) alone, metsulfuron (0.021 kg ai ha^-1) + dicamba (0.14 kg ai ha^-1), metsulfuron (0.021 kg ai ha^-1) + halosulfuron (0.053 kg ai ha^-1) + dicamba (0.14 kg ai ha^-1), metsulfuron (0.021 kg ai ha^-1) + sulfentrazone (0.070 kg ai ha^-1), metsulfuron (0.021 kg ai ha^-1) + sulfentrazone (0.070 kg ai ha^-1) + dicamba (0.14 kg ai ha^-1), and thiencarbazone + iodosulfuron + dicamba [Celsius (0.17 kg ai ha^-1)]. All treatments included a non-ionic surfactant (NIS) at 0.25% v/v. Treatments were applied on 29 July 2013 using a CO₂ pressurized backpack sprayer equipped with XR8004VS nozzle tips calibrated to deliver 375 L ha^-1 at 221 kPa. Virginia buttonweed cover was visually evaluated 1, 2, 4, and 8 weeks after initial treatment (WAT). Percent Virginia buttonweed control for each treatment was calculated relative to initial Virginia buttonweed cover. Analysis of variance was performed in SAS and means were separated according to Fisher’s protected LSD at the 0.05 significance level. No bermudagrass phytotoxicity was observed throughout the length of the trial, regardless of treatment. Virginia buttonweed control was 4 to 14% 1 WAT, regardless of treatment. At 2 WAT metsulfuron + halosulfuron + dicamba resulted in 100% Virginia buttonweed control. All other treatments resulted in 74 to 89% control 2 WAT. Metsulfuron + dicamba and metsulfuron + halosulfuron + dicamba resulted in 100% Virginia buttonweed control 4 WAT followed by (fb) metsulfuron + sulfentrazone (93%) fb metsulfuron (88%) fb Celsius (87%) fb metsulfuron + sulfentrazone + dicamba (80%). At 8 WAT significant Virginia buttonweed regrowth was observed, regardless of treatment. Metsulfuron + sulfentrazone resulted in the greatest Virginia buttonweed control (71%) 8 WAT. Metsulfuron + dicamba, metsulfuron + halosulfuron + dicamba, and metsulfuron + sulfentrazone + dicamba resulted in 65 to 68% control 8 WAT, regardless of treatment. Virginia buttonweed control in response to metsulfuron 8 WAT was reduced to 31%, while control with Celsius was reduced to only 9%.