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.

Resistance to Multiple PRE Herbicides in a Field-evolved Rigid Ryegrass (Lolium rigidum) Population

“…The level of resistance to prosulfocarb observed in this field-selected population was similar to a recurrently selected L. rigidum population of Busi and Powles (2013). The RIs for triallate and thiobencarb were slightly higher than for prosulfocarb and EPTC, which could be related to the differences in water solubility and binding capacity among the thiocarbamate herbicides tested (Mangin et al 2017; Westra et al 2014). The EP162 population displayed a level of trifluralin resistance similar to a recent report of 17-fold resistance conferred through a target-site point mutation in an L. rigidum population SLR74 (Fleet et al 2017) and consistent with reported resistance in field-collected populations from across South Australia (Boutsalis et al 2012).…”

Weed control under conservation agriculture in dryland smallholder farming systems of southern Africa. A review

“…Other studies have found that tillage can have both a negative and positive effect on weed seed banks: tillage may temporarily incorporate some weed seeds into deeper layers while bringing others to the soil surface where they are exposed to the conditions necessary for germination (Carter and Ivany 2006;Santín-Montanyá et al 2016). A study on wild oat (Avena fatua L.) in Alberta, Canada determined that tillage practices resulted in higher weed pressure for two reasons: first, tillage buried wild oat seeds deeper within the soil profile, thereby limiting their exposure to herbicides (Mangin et al 2016). Secondly, the relatively large seed size of wild oat allows it to germinate from greater depths within the soil, thus negating the benefits of burying the seeds through tillage (Ibid.).…”

Control of thiocarbamate-resistant rigid ryegrass (Lolium rigidum) in wheat in southern Australia

“…Reduced rainfall following herbicide application would therefore most likely be the cause of pyroxasulfone failure. Although thiocarbamate herbicides still have a rainfall requirement following application, they require less rainfall following application than pyroxasulfone (Mangin et al 2017). The uptake of thiocarbamate herbicides is also through both the shoots and roots (Fuerst 1987).…”