ILLINOIS TREES: THEIR Diseases 



J. CEDRIC CARTER 



MOST KINDS OF TREES in Illinois are subject to one or 

 more diseases. Some diseases cause little noticeable damage to the 

 trees. Others, by severely injuring leaves, twigs, branches, or 

 roots, cause stunting or, eventually, dying of the trees. The 

 most virulent or destructive diseases, such as elm phloem ne- 

 crosis, Dutch elm disease, and oak wilt, usually cause rapid dying 

 of trees. 



The value of trees for shade and ornamental purposes on 

 lawns and in recreation areas, for windbreaks, for erosion con- 

 trol, or for lumber and other wood products may be greatly re- 

 duced or destroyed by disease. Also, the removal or destruction 

 of trees killed by disease may be very costly to home owners, 

 park districts, forest preserve districts, or municipal govern- 

 ments. 



Most tree diseases that are of frequent occurrence in Illinois, 

 or that are widespread or destructive here, are described in this 

 publication. Included are diseases of both native and introduced 

 trees. Information is given on prevention or control of these 

 diseases, 



WHAT CAUSES TREE DISEASES? 



In a broad sense, diseases in trees are any conditions that 

 alter or prevent the expected normal growth. They may be either 

 infectious or noninfectious. 



Infectious Diseases 



The common causes of infectious diseases in trees are fungi, 

 bacteria, and viruses. Other causes are a few of the higher plants. 



Fungi. — The agents of the infectious diseases causing the 

 greatest amount of damage to trees are fungi. They lack the 

 green coloring matter called chlorophyll and are unable to man- 

 ufacture their own food. They obtain nourishment from other 

 living plants or from dead organic matter. Fungi that grow on, 

 or in, a living plant are called parasites, and the living plant is 

 called the host. Those that live on dead organic matter are called 

 saprophytes. 



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