LAUSR

Abstract Field studies were conducted on organic soils in Belle Glade, FL, in 2016 to 2017 to evaluate sugarcane tolerance and fall panicum control with topramezone applied alone or in combination with triazine herbicides (atrazine, metribuzin, ametryn). Treatments included topramezone (25 and 50 g ai ha–1) applied alone or in combination with atrazine (2,240 g ai ha–1), metribuzin (2,240 g ai ha–1), and ametryn (440 g ha–1) on four plant cane varieties to evaluate tolerance, and on second ratoon fields to determine efficacy on fall panicum control. Topramezone applied alone had no effect on sugarcane chlorophyll fluorescence (i.e., the ratio of variable fluorescence to maximum fluorescence), total chlorophyll, and carotenoid 7 to 28 d after treatment (DAT), suggesting sugarcane tolerance. Significant reduction of these parameters occured 7 to 14 DAT when topramezone (50 g ai ha–1) was applied with ametryn or metribuzin; however, reductions were not detected thereafter, indicating recovery. Sugarcane yield was not affected by topramezone applied alone or in combination with the triazine herbicides. Topramezone (50 g ai ha–1) plus metribuzin resulted in acceptable control of fall panicum (84%) with limited to no regrowth of meristematic tissue at sugarcane canopy closure, equivalent to 56 to 70 DAT. These results indicate that when sequential applications of topramezone, applied alone or in combination with these triazine herbicides, are required for efficacious weed control, topramezone applications alone can be made after 7 d, whereas the combinations can be made after 14 or 21 d, depending on sugarcane sensitivity. Nomenclature: Ametryn; atrazine; metribuzin; topramezone; fall panicum, Panicum dichotomiflorum Michx. PANDI; sugarcane (Saccharum spp., interspecific hybrids).