352 DISEASES OF ECONOMIC PLANTS 



been estimated at from 14 to 37 per cent of the crop, 

 Rain and moisture favor it. 



When very prevalent, the soil may become infected as 

 in typical soil diseases. The only hope seems to rest in 

 resistant strains. 



Anthracnose {Colletotrichum cereale Manns) . — The effect 

 of this disease upon oats is similar to that described for rye. 



Yellow leaf disease { H elminthosporium inconspicuum 

 C. & Ell. var. hrittanicum Grove). — Oat leaves with this 

 disease turn yellow and pale and develop dark l^rown 

 spore-bearing spots. Little is known as to its severity or 

 prevention. 



Powdery mildew. See wheat. 



RICE 



Blast, rotten neck {Piricularia Oryzce Cav.). — This is a 

 world-wide rice disease which in Italy is controlled by the 

 use of resistant varieties. It has probably been present 

 for many years in American rice sections, but did not 

 become of serious economic importance until about 1895. 

 Wliat seems to be the same disease occurs upon crab 

 grass, and apparently infection may come from this host. 

 It is reported from South Carolina and Louisiana, also 

 from Texas, where it has been serious. The disease occurs 

 upon upland as well as irrigated fields. 



The most characteristic symptom consists of lesions at 

 the sheath nodes just over the joints of the stem, at the 

 region where the stem comes to be the axis of the head 

 (the " neck region ") and at the points where the blades of 

 the leaves join their sheaths,^ appearing first as very small, 



1 Fulton, H. R., La. Agr. Exp. Sta. Bui. 105, April, 1908. 



