Brown spot, often overlooked, is one of the most damaging diseases affecting rice crops. Caused by a fungal pathogen, this disease impacts various parts of the plant, including leaves, sheath, and grains, leading to significant yield losses. Below is a brief overview of its impact, occurrence, and identification.

What It Does

1. Infection Areas:

   • The fungus infects the coleoptile, leaves, leaf sheath, panicle branches, glumes, and spikelets.

2. Observable Damage:

   • Numerous large spots appear on leaves, which can lead to leaf death.
   • Seeds may become unfilled, spotted, or discolored due to infection.

Why and Where It Occurs

1. Favorable Conditions:

   • High relative humidity (86−100%) and temperatures between 16−36°C.
   • Common in unflooded, nutrient-deficient soils or those with toxic accumulations.
   • Wet leaf surfaces for 8−24 hours enable infection.

2. Sources of Infection:

   • Infected seeds producing infected seedlings.
   • Volunteer rice plants, infected debris, and weeds.
   • Airborne spores spreading the fungus.

3. Critical Crop Stages:

   • The disease can occur at all stages but is most severe during maximum tillering to ripening stages.

How to Identify

1. Seedlings:

   • Small, circular, yellow-brown or brown lesions that girdle the coleoptile and distort leaves.

2. Leaves at Tillering Stage:

   • Lesions appear small, circular, and dark brown to purple-brown.
   • Fully developed lesions are oval with a light brown or gray center and reddish-brown margins.

3. Lesion Size and Appearance:

   • On susceptible varieties, lesions are 5−14 mm long, causing leaves to wilt.
   • On resistant varieties, lesions are small and pinhead-sized.

Brown spot is a pervasive disease that can cause extensive damage if left unmanaged. Farmers should focus on using healthy seeds, implementing proper nutrient management, and adopting resistant varieties to mitigate the disease's impact.