Brown Spot of Rice

  • Symptoms

  • Trigger

  • Biological Control

  • Chemical Control

  • Preventive Measures

Brown Spot of Rice

Cochliobolus miyabeanus

Fungus


In a Nutshell

  • Circular, brown necrotic spots with gray to white center and reddish margins on mature plants.
  • Discoloration of stems and leaves gradually turn yellow and wilt.

Hosts:

Rice

Symptoms

This disease is characterized by a wide range of symptoms. However, the presence of circular or oval brown spots with a yellow halo during tillering stage is the most visible sign of the infection. As they enlarge, a gray center develops in the middle of these spots and a reddish brown margin becomes visible. Discoloration of stems is another characteristic symptom. On susceptible varieties, lesions may reach a length of 5−14 mm and can cause leaves to wilt. On resistant varieties, the lesions are yellow-brown and pinhead-sized. Infection of florets leads to incomplete or disrupted grain filling and a reduction in grain quality.

Trigger

The symptoms are caused by the fungus, Cochliobolus miyabeanus. It can survive in seeds for more than four years and spread from plant to plant through airborne spores. Infected plants debris left in the field and weeds are other common ways to spread the disease. Brown spot can occur at all crop stages, but the infection is most critical from maximum tillering to ripening stages. The disease often occurs in fields with a mismanagement of soil fertility, mainly in terms of micronutrients. Significant control of brown spot has been achieved using silicon fertilizers. The use of a mixture of cattle manure and chemical fertilizers somewhat also reduces its severity. High humidity (86-100%), prolonged periods of leaf moisture and high temperatures (16-36°C) are very favorable for the fungi.

Biological Control

To be sure that the seeds are not contaminated, a seed bath in hot water (53 - 54°C) for 10 to 12 minutes is recommended. To improve the results, place the seeds for 8 hours in cold water before the hot water treatment.

Chemical Control

Always consider an integrated approach with both preventive measures and biological treatments if available. The best way to prevent the disease is to use fungicides (e.g., iprodione, propiconazole, azoxystrobin, trifloxystrobin) as seed treatments.

Preventive Measures

Acquire your seeds from certified sources if possible.,Plant resistant varieties, if available in your area.,Ensure a balanced nutrient supply and monitor soil nutrients regularly.,Monitor fields for signs of the disease from tillering stage.,For soils that are low in silicon, apply calcium silicate slag before planting.