Feral rye control in quizalofop-resistant wheat in central Great Plains.
Feral rye (Secale cereale L.) is one of the most troublesome winter annual grass weed species in semi-arid winter wheat (Triticum aestivum L.) production systems across the central Great Plains (CGP). Lack of effective herbicide options further complicates the selective control of feral rye in winter wheat. The main objectives of this research were: (a) determine the sensitivity response of 10 feral rye populations collected from Kansas wheat fields to quizalofop-p-ethyl in a dose-response assay, and (b) to determine the effectiveness of various rates and application timings (fall or spring) of quizalofop-p-ethyl for feral rye control in quizalofop-resistant winter wheat in the CGP. Dose-response assays indicated that all tested feral rye populations were highly sensitive to quizalofop-p-ethyl with GR90 values (doses of quizalofop-p-ethyl needed for 90% reductions in shoot biomass at 3 wk after treatment) ranging from 33 to 72 g a.i. ha-1. A field study conducted in Colorado, Kansas, and Oklahoma for a total of 5 site-years indicated that quizalofop-p-ethyl applied at ≥77 g a.i. ha-1 in the fall or spring provided season-long feral rye control at 92-100% in quizalofop-resistant winter wheat. Irrespective of tested rates and application timings, a quizalofop-p-ethyl treatment protected winter wheat yield loss of 17-27% due to reduced feral rye competition compared to the nontreated weedy check in Colorado and Oklahoma. Results suggested that quizalofop-p-ethyl at labelled use rates (77-92 g a.i. ha-1) applied in fall or spring can provide effective feral rye control in quizalofop-resistant winter wheat.