Pyrithiobac reduces control of green foxtail (Setaria viridis) and bristly foxtail (Setaria verticillata) by propaquizafop

Experiments were conducted to evaluate potential interactions between propaquizafop and pyrithiobac applied in mixture or in sequential applications on green foxtail (Setaria viridis) and bristly foxtail (Setaria verticillata). The effect of propaquizafop application rate and the effect of ammonium sulphate were also evaluated. Propaquizafop (75–150 g ai/ha) applied alone at the five- to six-leaf growth stage provided 86–99% control of green foxtail and 92–100% control of bristly foxtail. Mixtures of propaquizafop with pyrithiobac applied at the same growth stage provided lower control of green foxtail and bristly foxtail by 27–33% and 17–22%, respectively, compared with propaquizafop applied alone. Increased rates of propaquizafop in the mixtures or the addition of ammonium sulphate did not eliminate the observed reduced control of both species with the mixture of pyrithiobac. Sequential applications where pyrithiobac was applied three days or one day before the application of propaquizafop also showed lower control of both species compared with propaquizafop applied alone. However, sequential applications where pyrithiobac was applied three days or one day after the application of propaquizafop showed more effective control of both species compared with the mixture and equal control to that achieved with propaquizafop applied alone.