Effects of Cultivars and Fungicides on Rice Sheath Blight, Yield, and Quality

Area of Science:

• Agricultural Science
• Plant Pathology
• Agronomy

Background:

• Sheath blight, caused by Rhizoctonia solani, significantly impacts rice (Oryza sativa) yield and quality in the southern US.
• Current rice cultivars exhibit varying susceptibility, from moderately to very susceptible, necessitating effective disease management strategies.

Purpose of the Study:

• To evaluate the response of rice cultivars with different sheath blight susceptibility levels to artificial inoculation and fungicide applications.
• To determine the impact of sheath blight epidemics on rice grain and milling yields.
• To compare the efficacy of two fungicides, azoxystrobin and flutolanil, in managing sheath blight and mitigating yield losses.

Main Methods:

• Field plots were inoculated with Rhizoctonia solani at the panicle differentiation stage from 2003-2005.
• Sequential fungicide applications (azoxystrobin or flutolanil) were applied at midboot and 50-70% heading stages.
• Sheath blight severity, incidence, grain yield, and milling yield were assessed for different cultivars under inoculated and treated conditions.

Main Results:

• Inoculation significantly increased sheath blight severity and incidence, causing yield losses ranging from 4% (cv. Francis) to 21% (cv. Cocodrie).
• Fungicide treatments effectively reduced sheath blight incidence and severity across all tested cultivars.
• Azoxystrobin demonstrated superior efficacy over flutolanil in minimizing yield losses, except in the moderately susceptible cultivar Francis.

Conclusions:

• Fungicide applications can mitigate yield losses caused by sheath blight, with azoxystrobin generally being more effective than flutolanil.
• Developing sheath blight-resistant rice cultivars is essential for sustainable production, reducing reliance on fungicides and minimizing yield reductions.
• Cultivar susceptibility plays a key role in disease impact and fungicide response, highlighting the need for resistant varieties.