Differential efficacy of tralkoxydim and diclofop-methyl on a suspected resistant ryegrass (Lolium rigidum Gaud.) biotype

Abstract

The efficacy of herbicides belonging to the aryloxyphenoxy propionic acids and cyclohexanedione groups was determined on a suspected resistant ryegrass biotype (Lolium rigidum Gaud.). Ryegrass seed was collected in the Southern Cape and germinated in a glasshouse with a day/night temperature regime of 20°C/15°C. Herbicides were applied at the third leaf stage. Tralkoxydim (2-(1-[ethoxyimo)propyl]-3hydroxy-5-(2,4,6-tri methylphenyl)cyclohex-2-enone), (125, 250, 500 and 1250 g a.i. ha^-1) and diclofop-methyl (±)-2-[4-(2,4-dichlo-rophenoxy)phenoxy]propanoic acid (177.5, 355, 710 and 1775 g a.i. ha^-1) were applied. Three formulations of tralkoxydim (SC, EC and WG) were used in the study. Forty-four days after herbicide application, percentage control was measured by means of fresh plant mass. Less than 20 control was obtained with diclofop-methyl at rates up to 1775 g a.i. ha^-1 (seven times the registered rate). All the formulations of tralkoxydim provided excellent ryegrass control at 250 g a.i. ha^-1. Resistance to diclofop-methyl and susceptibility to tralkoxydim within a single L. rigidum biotype was established.