300 Diseases of Ecoiiomic Plants 



no halo. The spot is long and narrow, between the veins. 

 Anthracnose {Colletotrichum cereale). — The effect of this 

 disease upon oats is similar to that described for rye. Yellow- 

 leaf {Helminthosporium inconspicuum C. & E. var. brittani- 

 cum Grove). — Oat leaves turn yellow and develop dark, 

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

 or prevention. Powdery-mildew. See wheat. Ergot occurs 

 but rarely on oats. 



RICE ''' 



Blast, rotten-neck ^^^ (Piriculana oryzoe 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. What 

 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, 

 water-soaked, sunken spots on the node of the sheath. Spots 

 upon the neck are not water-soaked, and the skin does not 

 rupture until the head breaks off. Later the spot becomes 

 brownish or black, and similar discoloration runs upward and 

 downward. The affected stem tissue gradually extends 

 laterally, shrinks, and dies, cutting into or through the joint, 

 which results in an open wound. The region above the 

 wound becomes pale and dies. 



Upon young plants leaf spots occur, first brown with ashen 

 center, later coalescing and taking th(> whole leaf. If the 

 attack is early, the grain does not fill at all; if late, it may 



