CARTER: ILLINOIS TREES: THEIR DISEASES 



19 



(Fig. 19) . Some canker diseases may be indicated by the presence 

 of fungus fruiting bodies in the diseased bark. These fruiting 

 bodies may produce raised places or pustules in the bark (Fig. 

 19), or they may break through the bark surface and become 

 conspicuous as black spots or bumps (Fig. 20). 



Cankers confined to branches usually can be eliminated by 

 removal of the affected branches. Some cankers on the trunks 

 of trees can be successfully removed by surgery. Large or multi- 

 ple trunk cankers may result in severe girdling and subsequent 

 death of affected trees (Fig. 21). 



Gall. — Gall diseases, appearing as growths on tree roots 

 or stems, may be caused by fungi (Fig. 22), bacteria (Fig. 23), 

 or viruses that enter the trees through wounds. Development of 



Fifi. 21 (left). — (ankers which continue to enlarge year after year 

 may result in severe girdling and subsequent death of affected trees. 



Fig. 22 {right). — Galls or tumors on stems of trees vary in size from 

 small and relatively inconspicuous to very large and conspicuous. The large 

 gall shown above is on a white oak. 



