36 



ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 46 



Fig. 35 {left). — When a canker is removed, the diseased area should 

 be traced back to living bark. Edges of the living bark should be painted 

 with shellac or wound dressing to prevent drying of living tissues. 



Fig. 36 {right). — After the edges are painted, all of the discolored or 

 diseased bark is removed with a chisel or other sharp tool. 



cankers have been removed. After the disinfectant has dried, 

 paint the exposed wood with wound dressing (Fig. 37). Wounds 

 may need repainting once or twice a year to insure complete 

 protection from wood rot fungi and other wood-destroying 

 agents (Fig. 38) . To prevent spreading infectious agents to other 

 trees, disinfect the tools used in pruning diseased trees. Dena- 

 tured alcohol, used as a spray or dip, is a satisfactory disinfec- 

 tant. 



Resistance and Immunif-y 



Whenever it is feasible to do so, species of trees resistant 

 or immune to diseases should be used. Spiny Greek juniper, Hill 

 juniper, and Keteleer red cedar are reported to be resistant to 

 juniper blight. Other selections of red cedar have been reported 

 that show resistance to cedar-apple rust. Varieties of chestnut 

 have been developed which are resistant to chestnut blight. The 



