Resistance of little seeded canary grass (Phalaris minor Retz.) to ACC-ase inhibitors

Abstract

Since 1996, several incidents of poor weed control regarding little seeded canary grass (Phalaris minor Retz.) in wheat (Triticum aestivum L.) production have been reported from the Western Cape. Little seeded canary grass showed indications of resistance towards ACC-ase inhibitors. Seed from these suspected resistant biotypes as well as seed from a susceptible biotype were collected from mature surviving plants and transported to the Small Grain Institute, Bethlehem where herbicide resistance studies were done. Herbicides used during the study were diclofop-methyl, clodinafop-propargyl and iodosulfuron. Both diclofop-methyl and clodinafop-propargyl are ACC-ase inhibitors and iodosulfuron is an ALS-inhibitor. Significant differences in the degree of control were found between the susceptible and four resistant biotypes when treated with diclofop-methyl and clodinafop-propargyl. When treated with diclofop-methyl, the LD50 values for the resistant (PMR 1, PMR 2, PMR 3 and PMR 4) biotypes were 594, 700, 225 and 2673 g a.i.ha−1 respectively, whereas the LD50 value for the susceptible biotype was 184.4 g a.i.ha−1. The LD50 values for the PMR 1, PMR 2, PMR 3 and PMR 4 biotypes treated with clodinafop-propargyl, were 79, 94, 29 and 280 g a.i.ha−1 respectively, whereas the LD50 value for the susceptible biotype was 24 g a.i.ha−1. No significant differences could be found between the susceptible and resistant biotypes when treated with iodosulfuron. The LD50 values for the susceptible and resistant biotypes varied between 27.4 and 29.2 g a.i.ha−1. This is, therefore, the first report confirming P. minor resistance to diclofopmethyl and clodinafop-propargyl treatments in the Republic of South Africa.