This disease is characterized by a wide range of symptoms. However, the presence of circular or oval brown spots with a yellow halo during the 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. Stems also become discolored. 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. The infection of florets leads to incomplete or disrupted grain filling and a reduction in grain quality.
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 plant debris left in the field and weeds are other common ways to spread the disease. Brown spots 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 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.
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.
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.