Evaluation of post-emergence herbicides for the control of wild oat (Avena fatua L.) in wheat and barley in Argentina

Abstract Wild oat ( Avena fatua L.) is the most troublesome weed in cereal crops in Argentina. With the aim of studying the effects of different herbicides, doses, and wild oat growth stage at application on weed control and crop yield, field experiments were conducted in wheat and barley crops during three growing seasons in the south of Buenos Aires Province, Argentina. Treatments were post-emergence applications of new herbicide, pinoxaden + cloquintocet mexyl (5%–1.25%), at doses that ranged from 20 g to 60 g a.i. pinoxaden ha −1 , applied at two to three leaves and the beginning of tillering of wild oat. In addition, standard treatments were included and applied at the same wild oat growth stages. Diclofop methyl at 511 g a.i. ha −1 and fenoxaprop-p-ethyl at 55 g a.i. ha −1 were applied in barley. In wheat, diclofop methyl was replaced by clodinafop-propargyl + cloquintocet mexyl (24%–6%) at 36 g a.i. clodinafop-propargyl + 9 g cloquintocet mexyl ha −1 and in 2008/09 wheat experiments, iodosulfuron plus metsulfuron methyl (5%–60%) at 3.75 g a.i. ha −1  + 3 g a.i. ha −1 also was included. In both crops, pinoxaden at 30 g a.i. ha −1 and at higher rates, fenoxaprop-p-ethyl and clodinafop-propargyl gave the best control of wild oat. In 2006/07 wheat crops, treatments applied at tiller initiation provided better control than the early timing averaged across herbicides. However, wheat yield generally was greater with early application. In barley, wild oat control and crop yield were similar regarding time of application. Variations in crop yield were correlated with grain number m −2 both in wheat and barley, but relationships between both grain number and spikes m −2 and with grains per spike were identified only in wheat.