Influence of Seeding System Disturbance on Preplant Incorporated Herbicide Control of Rigid Ryegrass (Lolium rigidum) in Wheat in Southern Australia

Field experiments were conducted in 2008, 2011, and 2012 to investigate the interaction between seeding system disturbance and PPI herbicides on rigid ryegrass control in wheat. Of the herbicides examined, prosulfocarb + S -metolachlor, and pyroxasulfone provided ≥ 70% control of rigid ryegrass, irrespective of seeding system. In contrast, trifluralin was the least-effective herbicide against rigid ryegrass and was particularly ineffective when used with single disc (10% control) relative to the triple-disc seeding system (80%) in 2012. Trifluralin consistently reduced wheat density when incorporated using single discs (46 to 59%) but not do so with the triple disc or double-shoot knife-point systems. Although there were large differences in crop establishment because of herbicide phytotoxicity, that did not always translate into large differences in yield because wheat was able to recover from reductions in plant density by increasing the spike number per plant. Pyroxasulfone caused no damage to wheat and appeared to be the most suitable PPI herbicide for use with single-disc seeding systems.