104 DISEASES OF TROPICAL PLANTS CH . 



order named ; Gold, the finest variety, being the most 

 seriously affected. 



In Italy great progress has been made in introducing 

 resistant varieties. Several of these, notably Chinese, 

 Lencino, Birmania, and Vialone Nero, are very success- 

 fully grown. Experience to date indicates, however, 

 that all varieties tend to lose their resistance after about 

 two to twenty years of cultivation in the same locality. 

 Twelve of these varieties introduced into America in 

 1908 have so far proved ill adapted to the climate of 

 the Gulf and Atlantic coasts, although growing well in 

 California, where the culture of rice is just being intro- 

 duced. In Japan, according to Kawakami, the most 

 resistant varieties are Bungo, Kawase, Sekitori, and 

 Kanieji. 



Possible Methods of Control. Spraying once or 

 twice with Bordeaux mixture, just as the head is 

 emerging from the sheath, has successfully prevented 

 the most serious form of joint and "neck" blast. 

 Probably a sticky Bordeaux would do better, but the 

 ordinary Bordeaux sticks to the head, neck, ligule, and 

 joint regions, although not to the general surface of the 

 plant. But it is not practicable to spray a field crop 

 like rice. 



Farneti recommends seed selection by a specific- 

 gravity method involving the use of a 1 per cent 

 copper sulphate solution which, at the same time, 

 separates the grains by weight, disinfects their surfaces, 

 and separates most weed seeds. This treatment appears 

 to be based upon the theory that blast is transmitted at 

 least in part by seed, which seems probable but has not 

 been clearly demonstrated. 



Special local conditions sometimes admit of special 

 methods. Heavy nitrogenous fertilizing may be reduced 

 or omitted, always with beneficial effect ; in certain 

 localities the substitution of non-nitrogenous fertilizers 

 may be possible. Lime has been used with local success 

 in America and in Eussia. There is room for unlimited 

 experiment on the fertilization of rice soils, as local 



