Any practice which leads to aerobic conditions in the soil predisposes rice plants to rice blast disease. Drill seeding and draining for stand establishment or herbicide applications in water seeded systems increase the risk of infection and susceptibility to rice blast. Rice plants grown in deeper water exhibit increased resistance to the disease over those grown in shallower water depths. This is apparent when we often see localized increased disease severities associated with high spots within a field. From an irrigation standpoint, maintaining a deep continuous flood is the best option for minimizing the risk associated with rice blast disease.

Nitrogen fertility management and rice blast

The impact of fertility management on rice blast disease susceptibility may be easily seen in affected fields where excessive levels of nitrogen have been applied. Excessive nitrogen fertilizer rates lead to increased host susceptibility, disease incidence, and disease severity. Areas where leaf blast is so severe that plants are actually killed often occur in aqua overlaps in fields planted to less tolerant varieties such as M104 and M205.

Plant stress and rice blast

Any form of stress may predispose rice plants to rice blast disease. Even slight stress may significantly alter the plant’s ability to tolerate infection by the pathogen. Nutrient deficiencies such as potassium and silica have been shown to significantly increase rice blast disease incidence and severity around the world. Other common stresses that may impact disease tolerance in California may include salinity, extreme temperatures, and herbicide injury. Managing the rice crop to avoid plant stress is a significant and often overlooked tool in minimizing risk associated with rice blast disease.

Converging factors and rice blast

As you can see there are many factors that influence the incidence and severity of rice blast in a specific field. I have only scratched the surface and there are many other factors that play a role. Rice blast is a very complicated disease that has the ability to increase in incidence and severity very rapidly under the right conditions. Growers need to manage for this disease in a holistic approach rather than just relying on fungicide applications for effective management. Little changes here and there in cultural practices can add significantly to the management of this disease.