Early-season Weed Control in Direct-seeded Onion

Field research was conducted at the Oakes Irrigation research center near Oakes, ND, on ‘Sedona’ onion.  Micro-rate applications of bromoxynil and/or oxyfluorfen were compared to preemergence treatments using ethofumesate at 1.1 or 2.2 kg/ha or DCPA at 14.9 kg/ha for early season broadleaf control. Clethodim plus a petroleum oil surfactant, was added to each micro-rate application for grass control.  Onion seed was planted May 14 and harvested October 3. Herbicide applications were made May 22 (PRE-A), June 4 (flag leaf-B), June 12 (1.5 leaf-C), June 21 (2 leaf-D), June 27, (3 leaf-E), and July 2 (4 leaf-F) using a CO₂ pressurized sprayer equipped with 80º flat fan nozzles with a spray volume of 20 GPA and pressure of 40 psi. Treatments that included micro-rate bromoxynil during at least one of the application timings provided better common lambsquarters control throughout the trial compared to treatments without bromoxynil. In contrast, treatments with the micro-rate oxyfluorfen applied alone had poor common lambsquarters control. However, applying bromoxynil at the 70 g/ha followed by tank mixes of bromoxynil and oxyfluorfen at 70 g/ha provided the best common lambsquarters control compared to all other treatments. Applying bromoxynil at the 35 g/ha followed by tank mixes of bromoxynil and oxyfluorfen at 70 g/ha had significantly less control of common lambsquarters. The highest yielding treatment was when bromoxynil was applied at 70 g/ha followed by tank mixes of bromoxynil and oxyfluorfen at 70 g/ha with 82.3 T/ha. The lowest yielding treatment besides the untreated, which didn’t produce any marketable bulbs, was when bromoxynil was applied at 35 g/ha followed by tank mixes of bromoxynil and oxyfluorfen at 70 g/ha with 26.8 T/ha. The preemergence conventional treatment of ethofumesate at 1.1 kg/ha had the second highest yield of 70.6 T/ha.