424 



PLANTS AND MAN 



cut ends of infected trees, in insect tunnels, and under loose 

 bark. The only method of control is to locate and remove all 

 infected trees, as well as all trees weakened by drought or other 

 causes, which serve as breeding grounds for the insect carriers 

 of the disease. To control this disease, man power and money 

 must be available while the disease is still confined to the re- 

 stricted area within a one hundred mile radius of New York city. 

 A few isolated infections in Ohio, Indiana, Virginia, and Mary- 



FiG. 258. — Other plant diseases include ergot of rye (A) and numerous powdery 



mildews (B). 



land, have been supposedly eradicated. Unless controlled im^ 

 mediately, the elms, especially the highly prized American or 

 white elm may suffer the same fate as that of the American 

 Chestnut, which has been practically exterminated by another 

 Ascomycete disease, the Chestnut blight or bark disease. This 

 disease, referred to in the opening pages of this chapter, kills by 

 destroying the inner bark and cambium of the tree, thus girdling 

 it and causing death. 



The ERGOT OF RYE to which reference was made in the intro- 

 duction to this chapter, is another Ascomycete (fig. 258). Ergot 

 does not seriously affect the yield of the rye and other cereal 



