Timing of Fall Application of Pyroxasulfone for Weed Control in Field Pea at Hettinger, ND, 2025.

Timing and rate of fall application of pyroxasulfone was evaluated for both crop response and weed control in 2025 at Hettinger, ND (see Table 1 for treatments; Table 3 for description of applications). A fall application of glyphosate alone provided poor control of cheatgrass (30%). Application of glyphosate plus pyroxasulfone (Zidua SC) resulted in 92-97% control of cheatgrass and there was no difference between rate or timing. At 23 days after planting (DAP) Wild oat control with pyroxasulfone increased from 74 to 85% for 3 to 5 oz/A of Zidua SC at the September application and similarly from 74 to 86% for 3 to 5 oz/A of Zidua SC at the October application timing. After this evaluation, clethodim (Section 3) was applied over the entire trial to control grasses so there were no further evaluations. At 23 DAP, increasing Zidua rate increased kochia control and timing of application resulted in similar control in most cases. At 50 DAP, kochia control was also higher for the 5 oz/A rate of Zidua compared with 3 oz/A, with similar response in most cases for application timing. Wild buckwheat control was poor to fair regardless of Zidua application rate or timing. 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.