Studies were conducted in 2007 and 2008 to determine the effect of flumioxazin and S-metolachlor on Palmer amaranth control and ‘Beauregard’ and ‘Covington’ sweetpotato. Flumioxazin at 0, 91, or 109 g ai ha⁻¹ was applied pretransplant 2 d before transplanting alone or followed by (fb) S-metolachlor at 0, 0.8, 1.1, or 1.3 kg ai ha⁻¹ PRE applied immediately after transplanting or 2 wk after transplanting (WAP). Flumioxazin fb S-metolachlor immediately after transplanting provided greater than 90% season-long Palmer amaranth control. S-metolachlor applied alone immediately after transplanting provided 80 to 93% and 92 to 96% control in 2007 and 2008, respectively. Flumioxazin fb S-metolachlor 2 WAP provided greater than 90% control in 2007 but variable control (38 to 79%) in 2008. S-metolachlor applied alone 2 WAP did not provide acceptable Palmer amaranth control. Control was similar for all rates of S-metolachlor (0.8, 1.1, and 1.3 kg ha⁻¹). In 2008, greater Palmer amaranth control was observed with flumioxazin at 109 g ha⁻¹ than with 91 g ha⁻¹. Sweetpotato crop injury due to treatment was minimal (< 3%), and sweetpotato storage root length to width ratio was similar for all treatments in 2007 (2.5 for Beauregard) and 2008 (2.4 and 1.9 for Beauregard and Covington, respectively). Sweetpotato yield was directly related to Palmer amaranth control. Results indicate that flumioxazin pretransplant fb S-metolachlor after transplanting provides an effective herbicide program for control of Palmer amaranth in sweetpotato.

Nomenclature: Flumioxazin; S-metolachlor; Palmer amaranth, Amaranthus palmeri S. Wats. AMAPA; sweetpotato, Ipomoea batatas L. Lam. ‘Covington’, ‘Beauregard’.