Combined Application of Fluazinam With Triazole Fungicides Results in Synergistic Activity Against Fusarium Crown Rot

ABSTRACT Fusarium pseudograminearum infection, causing Fusarium crown rot, is an important limiting factor for wheat production. There are no resistant wheat cultivars, so control depends primarily on the application of chemical fungicides. Although the triazole fungicides are extremely effective against F . pseudograminearum , their single action site and continual use present a high risk of resistance developing. However, previous studies have shown that alternate or combined use of fungicides with different modes of action can significantly reduce this risk. The current study adopted a co‐toxicity coefficient approach to evaluate the effect of combining the diarylamine fungicide fluazinam with the triazole fungicides flutriafol, propiconazole and tebuconazole. The results not only confirmed that combined treatment with flutriafol and propiconazole provided effective control of F . pseudograminearum grown in vitro, but also showed that certain ratios of the fungicide mixtures resulted in synergistic activity, particularly the 7:3 ratio of fluazinam:flutriafol. Additional pot experiments conducted under greenhouse conditions found that this optimal ratio provided excellent protection against Fusarium crown rot, resulting in 63.2% control, significantly higher than that obtained when fluazinam (42.3%) or flutriafol (34.1%) was used individually, and the highest of any of the treatments evaluated. These results have important implications regarding the control of F . pseudograminearum , suggesting not only that the combination of fluazinam and flutriafol could provide more effective prevention and treatment of Fusarium crown rot, but also that combined application has the potential to extend the service life of both fungicides beyond that which might be expected if each were used in isolation.