Timing of Fall Application of Pyroxasulfone for Weed Control in Spring Wheat at Hettinger, ND, 2025.

Timing and rate of fall application of pyroxasulfone was evaluated for weed control in spring wheat at Hettinger, ND (see Table 1 for treatments; Table 2 for description of applications). A fall application of glyphosate alone provided poor to fair control of cheatgrass (68-78%). Application of glyphosate plus pyroxasulfone (Zidua SC) resulted in 93-99% control of cheatgrass and there was no difference between rate or timing. At 35 days after planting (DAP) Wild oat control with pyroxasulfone ranged from 87 to 96% and was generally similar when comparing rates and timing of application. Prior to harvest, at 102 DAP, wild oat control ranged from 76 to 88%. At 35 DAP, kochia control ranged from 71 to 84%, and control was similar in most cases when comparing rates and timings. At 102 DAP, kochia control was higher in most cases when applications were made in September than in October. Wheat yield was reduced only when no herbicide was applied or when glyphosate was applied alone in the fall. Application of Zidua in the fall improved spring wheat yield by nearly two times. It is generally recommended to apply herbicides for residual weed control in the fall after soil temperatures have fallen to 40 to 50 F. While average soil temperature was greater at the September application timing, the lack of rainfall after this earlier application was likely responsible for results being similar to the later application timing. In years with greater fall rainfall, weed control would likely be reduced at the earlier application timing due to increased degradation of the herbicide in the fall.