Rice blast is a common rice disease caused by a fungus. When the environmental conditions are suitable for the fungus to reproduce and the disease resistance of rice is poor, the fungus can infect all part of the rice plants and produce lesions or spots. The fungus then continuously produces spores on these lesions, which are dispersed in the air, spreading the disease. Rice blast is a dangerous threat to rice production regions worldwide, causing annual losses of about 10-30% of global rice production.

What causes rice blast disease?
Rice blast disease typically occurs in environments with large temperature differences between day and night, as well as warm and humid area with heavy dew in early morning. Besides, fields with high nitrogen fertilization, dense planting, and poor ventilation are susceptible cause severe infections.

In Taiwan, rice blast disease occurs mostly from February to June during the first crop season. At the second crop season, from July to November. Due to high temperatures, which are not suitable for the growth of rice blast fungus so there are few outbreaks at second crop.

Symptoms and signs of blast disease:

Rice blast can occur at any stage of rice growth, may infect all parts of the rice plant, but appearing on the leaves and panicles more often. Leaves blast inflection, initially small brown or black spots appear on leaves, which then expand into spindle-shaped lesions. At this time, the edges of the lesions turn reddish-brown with a yellow halo, while the center becomes gray or white. In severe cases, the leaves may wither or complete death. If the infection at panicles (panicle blast), the panicle lesions are usually dark brown or black. Later infection, cause the sterility of grains, means the grains will be empty.

Prevention and control measures:

(1) Choose varieties with disease resistance for planting.

(2) Disinfect rice seeds: Seed disinfection can prevent the spread of rice blast disease.

(3) Proper fertilization practice: Using high level of nitrogen fertilizer will reduce the plant resistance to disease and cause lodging, it is easier for the disease to occur. The appropriate ratio of nitrogen, phosphorus, and potassium fertilizer can reduce the damage caused by rice blast disease.

(4) Increase the row spacing: Enough plant spacing results in stronger and more disease-resistant rice plants. The direction of the rice rows also affects the ventilation in the field. Adopting the same direction as the seasonal wind can improve ventilation and reduce the spread rate of rice blast disease.

(5) Chemical control: Use approved pesticides from the plant protection manual to prevent rice blast disease.

For the rice blast disease, early prevention is better than treatment. In addition to the pesticide application, the proper use of fertilizer, reducing the number of seedlings per area, and increasing the plant spacing are also important things to do. Early prevention and control can effectively reduce the damage of rice blast disease to rice crops.