Amaranthus spp. Control and Sweetpotato Tolerance to Fluridone-containing Herbicide Programs

Field studies were conducted at the Pontotoc Ridge–Flatwoods Branch Experiment Station in Pontotoc, MS, USA and the Horticultural Crops Research Station in Clinton, NC, USA in 2015 to determine pigweed ( Amaranthus spp.) control and sweetpotato ( Ipomoea batatas ) crop response to fluridone herbicide. Treatments consisted of 168 g·ha −1 a.i. fluridone alone or tank-mixed with 54 g or 107 g·ha −1 a.i. flumioxazin applied pretransplanting, fluridone/flumioxazin combinations followed by (fb) a layby application of S -metolachlor (801 g·ha −1 a.i.), and 107 g·ha −1 flumioxazin alone pretransplanting with and without a layby application of S -metolachlor. Crop injury was minimal (≤7%), only observed in Mississippi, and transient. Nine weeks after transplanting (WAP), Palmer amaranth ( A. palmeri ) control in North Carolina was ≥95% with flumioxazin fb S -metolachlor and fluridone plus flumioxazin fb S -metolachlor. However, control with all other treatments ranged from 29% (fluridone alone) to 79% (fluridone fb S -metolachlor). Eight WAP, redroot pigweed ( A. retroflexus ) control in Mississippi ranged from 58% to 97%. Fluridone plus 107 g·ha −1 flumioxazin fb S -metolachlor provided the most control (97%), while all other treatments provided less control and were similar to one another. At both locations, season-long weed control was improved with a layby application of S -metolachlor, which resulted in increased jumbo and total yield. Although fluridone resulted in nominal sweetpotato injury in this study, it also provided minimal pigweed control when applied alone and provided only limited benefit when applied in combination with flumioxazin and fb S -metolachlor.