South Khorasan province of Iran is the largest producer of common barberry (Berberis vulgaris L.) in the world. The production and quality of common barberry shrub are affected by broad range of abiotic and biotic causal agents. Witches' broom rust caused by Puccinia arrhenatheri is one of the most important diseases of common barberry shrubs in South Khorasan province. A two years' field experiment carried out to study the control of barberry witches' broom rust using the Falcon (Tebuconazole + Spiroxamine + Triadimenol) at concentrations 0.6 and 1 ml L-1, Folicur 1 and 1.5 ml L-1, Amistar Xtra (Azoxystrobin + Cyproconazole) 0.75 and 1.2 ml L-1 and Tilt 0.5 and 1 ml L-1 at two locations of South Khorasan during 2018-2019 at the time of disease symptoms initiation as randomized complete block design. There was significant difference in witches' broom rust severity scores between the different fungicides and rates of application and control treatment. The results of combined analysis of variance showed that one-time application of Folicur at concentrations 1 and 1.5 ml L-1 were determined as the most effective in controlling the disease at the time of disease appearance, followed by Folicur 1 ml L-1, 1.5 ml L-1, Falcon 0.6 ml L-1, Amistar Xtra 1.5 ml L-1, Amistar Xtra 0.75 ml L-1, Falcon 1 ml L-1, Tilt 1 and 0.5 ml L-1. The highest and lowest disease severity were obtained in control and Folicur (1 ml L-1) treatments, respectively. Based on our findings retrieved from results of this study and field trials, Folicur at concentrations 1 ml L-1 and Falcon at concentrations 0.6 ml L-1 at the time of disease symptoms initiation to achieve efficient control and application of rotation of them to mitigate fungicide resistance development are recommended. Application of treatments including Folicur at concentrations 1 and 1.5 ml L-1 and Amistar Xtra at concentrations 0.75 ml L-1 were also significantly effective in decreasing the number of witches' brooms.
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