Tolerances of barley cultivars to post-emergence herbicides

Abstract

Sixteen spring barley cultivars were tested in southern New South Wales for their tolerances to 12 post-emergence herbicides applied at the recommended rates and at three times those rates. Examples of unsafe combinations of cultivars and herbicides (at recommended rates) that have a risk of crop damage in this environment include: Shannon with bromoxynil at 0.42 kg/ha; Panvan with bromoxynil plus MCPA at 0.42 + 0.42 kg/ha; Bandulla, Beecher, Clipper, Malebo, Panvan and Weeah with dicamba at 0.08 kg/ha; and Clipper, Galleon, Lara and Shannon with dicamba plus MCPA at 0.11 + 0.48 kg/ha. Severe damage occurred to barleys from diclofop-methyl at 0.56 kg/ha and from chlorsulfuron at 0.01 8 kg/ha. Cultivars which showed tolerance were Grimmett, Lara, Stirling and Shannon with chlorsulfuron, and Shannon and Weeah with diclofop-methyl. The use of rates three times those recommended by the manufacturers in these experiments identified the susceptibility of additional cultivars which could be at risk of crop damage from overdosing, incorrect timing of application, or adverse environmental conditions. For example, Lara and Corvette with bromoxynil at 1.26 kg/ha; Corvette and Shannon with bromoxynil plus MCPA at 1.26 + 1.26 kg/ha; Corvette, Cutter, Galleon, Lara, Panvan, Schooner, and Shannon with dicamba plus MCPA at 0.33 + 1.44 kg/ha. The grain yields ofall cultivars were unaffected by both rates of difenzoquat, diuron, linuron, methabenzthiazuron or 2,4-D. The risks of crop damage v. the benefits of weed control are discussed. Seasonal variation was observed in the herbicidexcultivar interactions and this variation was sometimes of a greater magnitude than the differences between the cultivars. An interaction was observed between the incidence of barley leaf scald (Rhynchosporium secalis) and treatment with chlorsulfuron or diclofop-methyl. Routine screening of herbicides and crop cultivars for dangerous interactions is recommended, and we need a greater understanding of the effects of environmental factors on plant responses to herbicides.