Bruna Ronning
Program Technician I
University of Arkansas System Division of Agriculture
Stuttgart, Arkansas, United States
Scott Belmar
Program Technician III
University of Arkansas System Division of Agriculture
Stuttgart, Arkansas, United States
Rodrigo Pedrozo
Postdoctoral Research Associate
USDA ARS Dale Bumpers National Rice Research Center (DB NRRC)
Stuttgart, Arkansas, United States
Jessica Harris
Program Technician I
University of Arkansas System Division of Agriculture
Stuttgart, Arkansas, United States
Alejandro Rojas
Assistant Professor
Michigan State University
East Lansing, Michigan, United States
Jarrod Hardke
Associate Professor
University of Arkansas System Division of Agriculture
Stuttgart, Arkansas, United States
Camila Nicolli, PhD
Assistant Professor - Extension Plant Pathologist
University of Arkansas
Stuttgart, Arkansas, United States
Sheath blight, caused by Rhizoctonia solani, is a major concern for rice production in Arkansas. Given growers' concerns about reduced fungicide effectiveness, this study compared the efficacy of azoxystrobin (QoI) and flutolanil (SDHI) on R. solani isolates by evaluating their mycelial growth on culture media. A total of 32 isolates (18 from 2023 season and 14 from 2024 season) were obtained from 18 counties in Arkansas. Molecular analysis identified all isolates to belong to the same anastomosis group (AG1-1A). Fungicide assays evaluated six concentrations ranging from 10,000 to 0.1 ppm for flutolanil (Elegia®) and azoxystrobin (Quadris®) amended with Salicylic hydroxamic acid (SHAM) and Propyl gallate (PG) to inhibit secondary respiration and ensured a specific response to the QoI fungicide. Mycelial growth was measured daily for four days at 25°C in the dark. Azoxystrobin varied by isolate, with the lowest sensitivity from Arkansas County (PP071) and the highest from Clay County (PP060). For isolates collected in 2024, the isolates from Randolph County (PP110) showed the highest sensitivity and a single isolate from Desha County (PP168) was the lowest. In contrast, all isolates were sensitive to flutolanil, at the lowest concentrations. These findings emphasize the importance of using fungicides with different modes of action for effective sheath blight control, particularly given the limited efficacy of azoxystrobin. Furthermore, this research provides valuable insights into fungicide efficacy and resistance management.