Azoxystrobin Rate and Timing Effects on Rice Sheath Blight Incidence and Severity and Rice Grain and Milling Yields

Area of Science:

• Agronomy
• Plant Pathology
• Agricultural Chemistry

Background:

• Rice (Oryza sativa) cultivation faces significant yield losses due to sheath blight.
• A lack of sheath blight resistant rice varieties necessitates chemical control measures.
• Fungicides are crucial for preventing reductions in grain and milling yield.

Purpose of the Study:

• To determine the optimal application rate and growth stage for a single foliar application of azoxystrobin.
• To evaluate the efficacy of azoxystrobin in controlling sheath blight in rice.
• To assess the impact of fungicide application timing on rice yield and milling quality.

Main Methods:

• Field trials were conducted from 2000 to 2002 with azoxystrobin applied at various rates (0.22, 0.17, 0.11 kg a.i. ha⁻¹) and growth stages (PD+7, Boot, Heading, Post-heading).
• Sheath blight severity and incidence were assessed before harvest.
• Grain yield and head rice milling yield were measured for each treatment group.

Main Results:

• A single azoxystrobin application between 7 days after panicle differentiation (PD+7) and heading significantly reduced sheath blight severity.
• Fungicide applications during this window led to significantly higher grain and head rice milling yields compared to untreated controls.
• Fungicide rates did not significantly affect outcomes when applied at PD+7, Boot, or Heading stages.
• Post-heading fungicide applications resulted in higher disease severity and lower yields than earlier applications.

Conclusions:

• Applying azoxystrobin between PD+7 and Heading is the most effective strategy for managing sheath blight in rice.
• Timely fungicide application can restore rice yield and milling quality to levels comparable to uninfected crops.
• Fungicide application timing is critical for maximizing disease control and yield benefits in rice production.