DISEASES OF RICE 99 



circulation of water, causing the plants to wilt, and 

 frequently results in death. It is especially severe on 

 seedlings. Mr. Butler, who has made extensive investi- 

 gations on this disease is of the opinion that it cannot be 

 controlled by any method other than the development 

 of immune varieties. 



DISEASES OF RICE 1 



Blast (Italian, brusone ; Japanese, imochibyo) (Figs. 

 46, 47) is the most serious disease of rice. It has been 

 studied in Japan, Italy, Russia, and North America, and 

 probably occurs wherever rice is grown. On account of 

 its obscure and protean character it usually is not 

 popularly recognised as a disease, but the damage is 

 attributed to weather or soil conditions, bad seed, or 

 bad water. It commonly occurs in epidemics, cul- 

 minating in a series of "bad years," followed by a 

 series of years in which only mild or local attacks occur. 

 No locality where it has once occurred appears to ever 

 become entirely free from it. Definite accounts exist of 

 its occurrence in Japan at least two hundred years ago, 

 and in Italy as early as 1560 ; probably it has existed 

 from very ancient times. From the standpoint of the 

 amount of loss it causes, it undoubtedly ranks with the 

 grain rusts as one of the most serious plant diseases of 

 the world. 



Cause and Symptoms. Blast is caused by the 

 parasitism of a fungus which has been called Piricularia 

 oryzae, Br. & Cav. The correct name of the fungus is 

 still somewhat in doubt, as it is apparently identical 

 with the fungi Dactylaria parisitans, Cav., and 

 Piricularia grisea, (Cke.) Sacc., both of which occur on 

 various grasses. This fungus may occur upon any part 

 of the rice plant except possibly the roots, and at any 

 age, thus producing the most diverse effects. 



In its most typical and disastrous form, blast is a 



1 This discussion of the diseases of rice was written by Dr. Haven Metcalf 

 of the United States Bureau of Plant Industry. 



