Evaluation of Rhyme Fungicide for Controlling Cotton Root Rot of Pistachio in Arizona, 2024

Cotton root rot (commonly known as Texas root rot, Ozonium root rot, Phymatotrichopsis root rot, or Phymatotrichum root rot), caused by Phymatotrichopsis omnivora, is a major soil-borne disease of pistachio in Arizona. The fungus produces necrotic lesions on the bark of the root and crown and destroys root systems, resulting in rapid tree decline and mortality. This report evaluates DMI fungicide flutriafol for the management of cotton root rot. The field trial was conducted in 2024 on 2-year-old Pistacia vera ‘Golden Hills’ trees on Platinum rootstocks. The results of this study provided efficacy and crop safety data to support the manufacturer’s registration of Rhyme fungicide for pistachios. Rhyme will be available to pistachio growers to manage cotton root rot and should reduce tree and yield losses.