CEREALS 



375 



Anthracnose {Colletotrichum cereale Manns). — This an- 

 thracnose seems to prevail on wheat as extensively as 

 upon rye. Upon wheat the head or parts of it are not 

 destroyed, as in the case of rye, but general weakness of 

 the plant and light shriveled grain follows the attack. 



Powdery mildew (Erysiphe graminis DC). — The usual 

 characters of the powdery mildews are exhibited : a whitish, 



Fig. 160. — Normal wheat kernels and shriveled kernels due to anthracnose. 

 After Manns. 



flour-like coating in irregular circular spots upon the leaves 

 and other plant parts. This mildew, together with the 

 mildew of oats, rye, and barley, bears the same specific 

 name, but upon each of these crops the form is so special- 

 ized as not to transfer readily, if at all, to the other crop 

 plant. Thus from the plant disease viewpoint there are 

 practically four distinct kinds of mildew, although indistin- 

 guishable to the eye. The form upon wheat grows upon all 

 species of Triticum. 



In damp, shaded spots the mildew is sometimes quite 

 injurious, though it is rarely so over an}' considerable 

 area. The conditions favoring the disease should be 

 avoided. 



