Rice Blast

(also rotten neck), a serious disease of rice caused by the imperfect fungus Piricularia oryzae. Rice blast occurs in rice-growing regions throughout the world. It is characterized by the formation of variously shaped and colored spots on the leaves, leaf sheaths, stem axils, panicles, and seeds. The leaves die, the stems break, and the panicles dry prematurely or form undersized seeds. The disease causes greatest harm during heading and flowering. Harvest losses are 15 to 40 percent, and the quality of the grain is significantly lowered. When the disease is epiphytotic, the plants die.

The causative agent of rice blast has several generations during the vegetative period and spreads by means of conidia; it winters in the form of mycelium on post-harvest remains (one to three years) and in seeds. The disease develops when there is high air humidity (no lower than 88 percent) and high temperature (15° to 35°C). The infection may be transmitted with irrigation water. Wild rice and other grains may be reservoir hosts of the disease. Control measures include cultivating resistant varieties, plowing under live remains, burning the stubble on areas with severe development of the disease, and treating infected plantings and rice seeds with fungicides.