Influence of Tillage on Control of Wild Oat (Avena fatua) by the Soil-applied Herbicide Pyroxasulfone

Abstract

Wild oat control options are limited in western Canada due to resistance to most common herbicides. Control of wild oat with pyroxasulfone, a soil-applied, very-long-chain fatty-acid inhibitor, was investigated. A series of greenhouse and field experiments were conducted to isolate the effects of vertical seed position, site of herbicide interception, and tillage on wild oat control with pyroxasulfone in comparison with triallate. In greenhouse experiments, wild oat shoot length (soil surface to leaf tip) was reduced (P<0.05) in shallow-seeded wild oat compared with deep-seeded wild oat with pyroxasulfone (6.2 and 9.8 cm, respectively) and triallate (3.7 and 13.2 cm, respectively). Soil-applied pyroxasulfone remained in the top 2.5 cm of the soil with or without a simulated rainfall event. Pyroxasulfone was most effective if either the seed or the shoot 1 cm above the seed intercepted the herbicide layer. If a wild oat emerges from deeper in the soil profile, the sensitive part of the seedling may not intercept an effective rate of pyroxasulfone in the soil. In field experiments comparing deep- and shallow-seeded wild oat treated with pyroxasulfone and triallate in fields with and without tillage, there were no significant effects of tillage alone on wild oat shoot length. Deep-seeded wild oat emerged early, and while herbicides reduced shoot growth, shoots were >10 cm. Shallow-seeded wild oat had delayed emergence, possibly due to reduced soil moisture, and herbicides reduced shoot growth to <10cm. Pyroxasulfone is likely to be more effective in no-till fields where wild oat seeds are not located deep in the soil.