Our experiences with acifluorfen in sugarbeet.
Acifluorfen for control of glyphosate resistant (GR) waterhemp (Amaranthus tuberculatus) in sugarbeet was evaluated in Minnesota and North Dakota in 2019, 2020, and 2021. Acifluorfen at 0.28 kg ha-1 plus non-ionic surfactant (NIS) at 0.125% v/v or acifluorfen mixtures with glyphosate (PowerMax) at 0.28 + 1.10 kg ha-1 controlled waterhemp escapes up to 10-cm tall once sugarbeet reached the 6-lf stage using ground application methods in a minimum of 140 L ha-1 water carrier with nozzles delivering a medium droplet spectrum. Acifluorfen was applied on over 150,000 ha following Environmental Protection Agency (EPA) approval of a Section 18 emergency exemption in 2021 and 2022. In addition to waterhemp size, sugarbeet must be greater than the 6-lf stage at application to avoid detrimental sugarbeet injury and root yield loss. Evaluation of sugarbeet tolerance and waterhemp control is on-going. The likelihood for sugarbeet injury was greater when day-time maximum air temperatures were greater than 29C, when sugarbeet was less than 6-lf stage, and/or when glyphosate was mixed with acifluorfen. Likewise, waterhemp regrowth has been observed when waterhemp size was greater than 10-cm or when sugarbeet partially shielded targeted waterhemp. Field experiments in 2022 a) evaluated sugarbeet tolerance from single or repeat acifluorfen application alone or in mixtures with glyphosate and adjuvants and b) evaluated optimizing carrier volume and spray nozzles to improve waterhemp control. Experiments were planted at seven locations in Minnesota between May 16 and June 3, 2022. Sugarbeet injury, root yield, and percent sucrose from glyphosate (PowerMax3) at 1.05 kg ha-1 with NIS and ammonium sulfate was applied at the 2- and 6-lf sugarbeet stage and was compared to sugarbeet injury, root yield, and percent sucrose from a single acifluorfen application at 0.28 kg ha-1 with NIS at 0.25% v/v or crop oil concentrate at 1.17 L ha-1 at the 6-lf stage, acifluorfen at 0.21 kg ha-1 with NIS at 0.125% v/v at the 6-lf stage followed by a repeat acifluorfen application and NIS seven days later, and acifluorfen applied in mixtures with glyphosate with AMS or with AMS and NIS at the 6-lf stage. Repeat acifluorfen applications or acifluorfen mixed with glyphosate increased sugarbeet necrosis or growth reduction injury as compared to glyphosate. However, acifluorfen alone did not reduce root yield as compared to the glyphosate control treatment. Acifluorfen mixtures with glyphosate reduced or tended to reduce root yield and recoverable sucrose ha-1 but did not reduce percent sucrose as compared to glyphosate or acifluorfen alone. Carrier volume or spray nozzle did not affect sugarbeet injury, although acifluorfen applied through flat fan nozzles tended to increase sugarbeet injury as compared to other nozzles evaluated. Waterhemp control was best when acifluorfen was applied at 187 L