Verticutting Prior to Herbicide Application Enhances Dallisgrass Control.

Field experiments were conducted at the Pine Hills Golf Club in Winder, GA during the summer of 2013 to investigate the impact of verticutting on the efficacy of several herbicides for the control of dallisgrass (Paspalum dilatatum Poir.). The trial was located on a common bermudagrass rough (5.1 cm) with naturally occurring infestations of dallisgrass. Plots measuring 1.5 x 1.5 m were arranged in a 2 x 5 factorial within a randomized complete block design with four replications. The main factor was cultivation (verticutting or no cultivation) and the sub-factor was herbicide treatment. The trial site was mowed to 5.1 cm 48 hours before trial initiation. On June 14, 2013 half of the site was verticut in two directions to a depth of 2.5 cm. The entire site was raked and all debris was removed. Herbicide treatments were initiated the same day with a sequential applied on August 28, 2013. Treatments consisted of Tribute Total (thiencarbazone + foramsulfuron + halosulfuron) at 0.136 kg ai ha^-1 fb Tribute Total at 0.136 kg ai ha^-1, Celsius (thiencarbazone + iodosulfuron + dicamba) at 0.171 kg ai ha^-1 + Revolver (foramsulfuron) at 0.073 kg ai ha^-1 fb Celsius at 0.171 kg ai ha^-1 + Revolver at 0.073 kg ai ha^-1, MSMA at 2.5 kg ai ha^-1 fb MSMA at 2.5 kg ai ha^-1, and Certainty (sulfosulfuron) at 0.066 kg ai ha^-1 + MSMA at 2.5 kg ai ha^-1 fb Certainty at 0.066 kg ai ha^-1 + MSMA at 2.5 kg ai ha^-1. Each treatment was applied with methylated seed oil (MSO) at 0.5% v/v. A non-treated check was added for comparison. Treatments were applied using a CO₂ pressurized backpack sprayer equipped with XR8004VS nozzle tips calibrated to deliver 375 L ha^-1at 221 kPa. Verticutting was not performed prior to sequential herbicide applications. Visual ratings of % bermudagrass phytotoxicity and % dallisgrass cover were recorded. Percent bermudagrass phytotoxicity was rated on a scale of 0 (no bermudagrass phytotoxicity) to 100% (complete bermudagrass desiccation) 1 and 2 weeks after each treatment. Percent dallisgrass cover was recorded 8 and 16 weeks after initial treatment (WAIT). Percent cover was compared back to dallisgrass cover recorded at the initiation of the trial and converted to % dallisgrass control. The only bermudagrass phytotoxicity (≤ 10%) was observed in response to MSMA following initial applications. However, plots fully recovered by 3 WAIT. Verticutting increased dallisgrass control in response to Tribute Total and Celsius + Revolver from 60% (no cultivation) to 86% and 88% (verticutting) control 8 WAIT, respectively. In contrary, verticutting decreased control in response to MSMA and Certainty + MSMA from 28% and 59% (no cultivation), respectively to 4% (verticutting) control 8 WAIT. Verticutting did not improve dallisgrass control in response to any herbicide treatments 16 WAIT. Dallisgrass control in response to Tribute Total and Celsius + Revolver without cultivation was 96 and 98% 16 WAIT, respectively. Certainty + MSMA without cultivation resulted in 89% dallisgrass control, while control with MSMA alone was 63% 16 WAIT. Plots will be rated again in spring in order to determine the effect of cultivation on long-term dallisgrass control.