Efficacy of Fall- and Spring-Applied Pyroxasulfone For Herbicide-Resistant Weeds in Field Pea

Abstract

Field trials were initiated in fall 2011 to determine the potential of pyroxasulfone to control acetolactate synthase (ALS) inhibitor-resistant weeds in field pea. Pyroxasulfone was applied in split-plot trials at five locations in western Canada using fall and PRE spring applications of 0 to 400 g ai ha−1. Trial locations were chosen with a range of soil organic matter content: 2.9, 4.3, 5.5, 10.5, and 10.6% at Scott, Kernen, Kinsella, Melfort, and Ellerslie, respectively. The herbicide dose required to reduce biomass by 50% (ED50) in false cleavers ranged between 53 and 395 g ha−1at Scott and Ellerslie, respectively. Wild oat ED50s varied between 0.54 g ha−1at Scott in the fall and 410 g ai ha−1in the spring at Melfort. ED50s for wild oat and false cleavers varied by 7.4- and 746-fold, respectively, depending primarily on the organic matter content at the trial location. The effect of application timing was not consistent. Significant yield reductions and pea injury occurred at 150 and 100 g ha−1and higher at Kernen and Scott, respectively. Low organic matter and high precipitation levels at these locations indicates increased herbicide activity under these conditions. Pyroxasulfone may allow control of ALS inhibitor-resistant false cleavers and wild oat; however, locations with high soil organic matter will require higher rates than those with low organic matter for similar control levels.

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

“…Herbicides with low water solubility, like pyroxasulfone, have limited ability to penetrate the soil profile. High organic matter will reduce efficacy (Tidemann et al 2014). For adequate control, wild oat seeds need to germinate either in the concentrated herbicide layer or within 1 cm below it to allow for effective herbicide interception by the seedling.…”

“…Pyroxasulfone has a low water solubility of 3.49 mg L −1 at 20 C, and there is a strong correlation between soil binding, reduced herbicide dissipation, and increased soil organic matter content (Westra et al 2014). Higher rates of pyroxasulfone were required to achieve similar control of wild oats and false cleavers ( Galium spurium L.) at locations in Alberta and Saskatchewan as soil organic matter increased (Tidemann et al 2014). Szmigielski et al (2014) measured pyroxasulfone bioactivity across 25 different prairie soils and reported decreased activity in soils with low pH, although Westra et al (2014) observed no correlation between soil adsorption and soil acidity.…”

Tolerance of flax (Linum usitatissimum) to fluthiacet-methyl, pyroxasulfone, and topramezone

“…Despite any initial injury or reduction in flax density at most sites, pyroxasulfone did not significantly reduce crop height, yield, or TSW. While pyroxasulfone can control a broad range of weed species, efficacy can be largely influenced by site-year and environmental conditions (Tidemann et al 2014). For example, pyroxasulfone had the greatest control of Italian ryegrass (Lolium perenne L. spp.…”

Influence of tillage, vertical seed distribution, and pyroxasulfone application timing and rate on control of wild oat (Avena fatua L.)

“…In untilled soil with more soil moisture, the effect of application was significant (p < 0.05) for all pyroxasulfone rates. Previous studies of pyroxasulfone control of wild oat in Alberta and Saskatchewan showed an inconsistent effect of application timing at various locations (Tidemann et al 2014). Lower effective dose (ED 50 ) values, indicating greater inhibition by pyroxasulfone, were observed in fallapplied pyroxasulfone for two out of five sites and in the spring-applied pyroxasulfone for one site.…”

“…for control is critical (Beckie et al 2013). Pyroxasulfone is a soilapplied very-long-chain fatty acid inhibitor (Group 15) that has potential to be used for control of wild oat in western Canada (Tanetani et al 2009;Tidemann et al 2014). Acceptable tolerance had been reported in corn, soybean, sunflower, and field pea, while the weed spectrum includes small-seeded broadleaves and grasses (Tanetani et al 2011).…”