Herbicide resistant barnyardgrass in Iran and Turkey

Background: Inconsistent control of Barnyardgrass has been reported repeatedly by farmers in major rice growing areas of Iran and Turkey. Objective: Thus, a greenhouse study was conducted to investigate the resistance of Barnyardgrass to acetyl CoA carboxylase (cyhalofop-butyl) and acetolactate synthase (penoxsulam, bispyribac-sodium) inhibiting herbicides. Methods: The seeds were sown in pots in a greenhouse and after screening, were sprayed with various rates of cyhalofop-butyl, penoxsulam and bispyribac-sodium herbicides at 3-4 leaf stage. Four weeks later, the above ground biomass was cut, dried in an oven and weighted. The results were then analyzed in the R software (drc package) using a four or three parameter log-logistic function. All experiments were repeated twice. Results: While 30% of biotypes collected from Turkey were not controlled by ACCase inhibitors at twice the recommended rates, no resistance was observed in Iran’s samples. Only one biotype exhibited cross-resistant to penoxsulam and bispyribac-sodium in Iran, which was due to consecutive application of herbicides with modes of action similar to these herbicides. In contrast, several Turkish biotypes showed cross-resistance as well as multiple resistance to ACCase and ALS inhibitors. Conclusions: The rapid expansion of herbicide resistance in both countries indicate the necessity of adopting integrated weed management practices to hinder the further evolution of resistance in future.