The Relative Response of Two Foxtail (Setaria) Species to Diclofop

Abstract

ED50values (the dosage required to reduce the posttreatment gain in dry weight by 50%) for diclofop applied to green and yellow foxtail [Setaria viridis(L.) Beauv. ♯3SETVI andS. lutescens(Weigel.) Hubb. ♯ SETLU] at the two- and four-leaf stages were calculated from linear regression equations derived by plotting the logarithm of the applied dosage against the relative growth reduction expressed as a probit value. At the two-leaf stage, green foxtail was more susceptible to the chemical than yellow foxtail but at the four-leaf stage there was no significant difference in response of the two species. At least part of the difference in sensitivity of the two species at the two-leaf stage could be accounted for by differences in spray retention, with green foxtail retaining 1.8 times (expressed as μL/cm2) or 3.5 times (expressed as μL/g dry weight) as much spray as yellow foxtail, despite the fact that yellow foxtail had a greater projected leaf area. At the four-leaf stage, the amount of spray retained by both species calculated on a per gram dry-weight basis was significantly less than at the two-leaf stage, accounting in part for the higher ED50values obtained at the later growth stage. However, there appeared to be no direct relationship between the amount of spray retained and the comparative growth response of the two weeds at the later stage of application.

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

“…Miller and Alley (1987) made a similar observation, noting that increased herbicide rates were required to achieve comparable control when applied at later growth stages. Similar responses have been observed with cyclohexendione and aryloxyphenoxy propionate herbicides (Harker and Blackshaw 1991;Klingaman et al 1991;Morrison and Maurice 1984;Schreiber et al 1979;Todd and Stobbe 1977).…”

“…The lack of a direct relationship between herbicide efficacy and wild oat growth stage indicates that other factors may overshadow growth stage as a determinant of herbicide efficacy. Although several studies have demonstrated the importance of weed growth stage on imazamethabenz and diclofop performance (Harker and O'Sullivan 1991;Miller and Alley 1987;Morrison and Maurice 1984;Schreiber et al 1979;Todd and Stobbe 1977), these results indicate that environmental conditions and weed demographics may be equally important.…”

Influence of AE F130060 03 Application Timing on Italian Ryegrass (Lolium multiflorum) Control1

“…Weed growth stage can have an impact on the efficacy of annual grass herbicides used in cereals (Blackshaw and Harker 1996). Diclofop was more effective on green foxtail (Setaria viridis L.) when applied at an early growth stage (Morrison and Maurice 1984). Similarly, imazamethabenz was more effective on wild oat (Avena fatua L.) when applied at early growth stages (Harker and O'Sullivan 1991;Pillmoor and Caseley 1984).…”

Diclofop-Resistant Italian Ryegrass (Lolium multiflorum) Control in Imidazolinone-Tolerant Wheat

“…Single applications of imazamox at either 36 or 54 g/ha controlled Italian ryegrass better when applied POST1 than POST2 because of weed size at herbicide application; however, control from these treatments was no more than 68% 150 DAE (Table 2). Weed growth stage can influence the efficacy of annual grass herbicides used in cereals (Blackshaw and Harker 1996;Harker and O'Sullivan 1991;Morrison and Maurice 1984). Imazamox at 54 g/ha controlled more Italian ryegrass than imazamox at 36 g/ha at both the POST1 and POST2 timings.…”