Lolium spp. resistance to ACC-ase inhibitors in wheat (Triticum aestivum L.) within the RSA: a preliminary study

Abstract

Herbicide resistance raises the possibility that the agricultural industry and crop producers might loose a valuable chemical tool that is essential for the control of weeds in wheat (Triticum aestivum L.) production. The recognition of herbicide resistance occurred relatively recently (1960), despite the widespread use of selective herbicides worldwide. Resistant biotypes of Averta fatua L. to diclofop-methyl (±)2-[4-(2,4dichlorophenoxy)phenoxy]propanoic acid were confirmed in the western Cape. Recently, farmers and chemical companies reported resistance of Lolium spp. to several selective herbicides in small grains in the western Cape. The main objective of the present study was to assess resistance of Lolium spp. against ACC-ase inhibitors used in wheat production. Seed of Lolium spp. which were suspected to be resistant was sown in pots in a glasshouse at a temperature regime of 15°C/20°C (night/day). During the 2–4-leaf stage, the plants were sprayed with four herbicides viz. diclofop-methyl, clodinafop-propargyl (2-propynyl (R)2-[4-(5-chloro-3-fluoro-2-pyridinyloxy)-phenoxy-pro pionate], tralkoxydim (2-(1 [ethoxyimo)propyl]-3-ktydroxy-5-(2,4,6-trimethylphenyl)cyclohex-2-enome) and imazamox, 2[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-5-(methoxymethyl)-3pyridinecar bolic acid at double the registered rates. Four weeks after herbicide application, percentage control was measured by comparing fresh plant mass. This study confirmed resistance of Lolium spp. to ACC-ase inhibitor graminicides registered for use in wheat in the western Cape.