CARTER: ILLINOIS TREES: THEIR DISEASES 



orders are called physiological diseases. A common type of phys- 

 iological disease of trees in Illinois is chlorosis, often seen in the 

 pin oak. This disease is usually associated with a deficiency of 

 available iron in the soil. Other unfavorable environmental 

 conditions are associated with weather — too much or too little 

 moisture, too high or too low temperatures. The resulting dis- 





Fig. 7 (left). — Sapsuckers, in feeding on the sap of trees, maiie bands 

 of conelike holes in the bark of branches and trunks. These holes become 

 larger and somewhat rectangular or square, as shown in this picture, as the 

 injured tree continues to grow. Branches and trunks girdled by numerous 

 rows of these holes may die. 



Fig. 8 (right). — Mechanical injury to trees, especially to weakened or 

 newly transplanted trees, may be caused by bark beetles, borers, and other 

 insects. This picture shows galleries made by the smaller European elm 

 bark beetle in a weakened elm. 



