Influence of Application Timing on the Efficacy of Reduced Rate Postemergence Herbicides for Wild Oat (Avena fatua) Control in Spring Barley (Hordeum vulgare)

Abstract

Field experiments were conducted during 1992 and 1993 at Kalispell and Moccasin, MT, to determine the influence of application timing on the efficacy of reduced rate postemergence applications of imazamethabenz and diclofop in spring barley. Herbicides were applied at their respective 1 × and ½ × use rates at either 1, 2, or 3 weeks after crop emergence (WAE). While excellent wild oat control was sometimes achieved with reduced rates, there was no consistent relationship between wild oat growth stage and the level of control at either site regardless of the herbicide or rate applied. This response suggests that efficacy is governed not only by wild oat growth stage, but also by weed demographics and environmental considerations. Barley yield and adjusted gross return values were highest at Kalispell when imazamethabenz treatments were applied at 1 WAE, regardless of the level of wild oat control. Adjusted gross return values were similar for the 1 × and ½ × imazamethabenz treatments. Yields and adjusted gross returns with diclofop treatments were more related to the level of wild oat control at Kalispell, with the 1 × diclofop treatments providing the greatest yields and adjusted gross return values. The level of wild oat control at Moccasin had minimal effect on barley yield and adjusted gross returns, with both values being comparable to the nontreated check.

Effect of reduced doses of mesosulfuron + iodosulfuron to control weeds in no-till wheat under Mediterranean conditions

“…The results of these trials also confirm the findings of several studies carried out by various researchers (Devlin et al, 1991;Spandl et al, 1997;Stougaard et al, 1997;Fernández-Quintanilla et al, 1998;Brian et al, 1999;Navarrete et al, 2000;Zhang et al, 2000;Boström and Fogelfors, 2002;Hamill et al, 2004) that maximum weed control is not always necessary to achieve the yield potential of the crop and that the use of below-labelled doses of herbicides can be an effective way of reducing pesticide input in field crops while maintaining satisfactory weed control. …”

“…As reported by other authors (Devlin et al, 1991;Spandl et al, 1997;Stougaard et al, 1997;Fernández-Quintanilla et al, 1998;Brian et al, 1999;Navarrete et al, 2000;Zhang et al, 2000;Boström and Fogelfors, 2002;Hamill et al, 2004) satisfactory control of weeds can be achieved by lower than normally recommended herbicide doses while maintaining acceptable crop yields. The results obtained in this study demonstrate that the success of reduced doses of the herbicide depends not only on early application, when the weeds are more sensitive, but also on the type of weeds present.…”

“…Several studies have demonstrated satisfactory weed control and acceptable crop yields, when herbicides are used at lower than normally recommended doses (Devlin et al, 1991;Spandl et al, 1997;Stougaard et al, 1997;Fernández-Quintanilla et al, 1998;Brian et al, 1999;Navarrete et al, 2000;Zhang et al, 2000;Boström and Fogelfors, 2002;Hamill et al, 2004). Herbicides at reduced doses are often sufficient to control weed density at or below the threshold levels.…”

Influence of variable rates of imazamethabenz and difenzoquat on wild oat (Avena fatua) seed production, and wheat (Triticum aestivum) yield and profitability

“…However, several other factors including water quality, carrier volume, wild oat growth stage and/or location, year and environmental factors also influenced the efficacy of low rates of several graminicides (Spandl et al 1997;Stougaard et al 1997;Stougaard 1999;Stevenson et al 2000). There is also anecdotal evidence that efficacy (and crop tolerance), even at recommended herbicide rates, can vary with year and location probably due to variable edaphic and climatic factors.…”

Control químico de la navajuela (Scleria melaleuca Rchb.f.ex.Schltdk.Cham.) en diferentes estados de desarrollo

“…Varios estudios han demostrado que el estado de desarrollo de la maleza en el momento de la aplicación infl uye de manera directa en la efi cacia del método de control empleado (Stougaard et al 1997, Hager et al 2003, Krausz et al 2000. En general, las recomendaciones de aplicación de los herbicidas indican que la planta que se desea controlar debe estar en crecimiento vegetativo activo y que no haya alcanzado su etapa de fl oración.…”