22 DISEASES OF ECONOMIC PLANTS 



cient to warrant the necessary outlay of labor. It is so 

 practiced as to remove the diseased wood and sufficient of 

 the healthy wood to expose an entirely uncontaminated sur- 

 face. The wounded surface is then treated with a strong 

 antiseptic (tar, bluestone, or corrosive subhmate), and if 

 the wound be deep, it is filled with cement to remedy any 

 mechanical weakening incident to the operation. 



6. Removal and destruction of diseased twigs, leaves, 

 or fruit. — Examples : pear blight, peach rot. The re- 

 moval and destruction of diseased parts diminishes the 

 nmnber of bacteria, spores, etc., that are available to spread 

 the disease and thus lessens infection. Mummified fruit 

 may be picked from the plant or the ground and destroyed, 

 or it may be removed by appropriate pasturage by fowls, 

 swine, etc. Affected leaves in many instances may be 

 similarly removed. Blighted twigs and cankers may be 

 cut out at any time when they are seen. 



7. Removal, in whole or in part, of complementary hosts. 

 — Examples : apple rust, wheat rust. Complementary hosts 

 always serve as multiplying places for the causal parasite, 

 and in some instances are absolutely essential to its hiberna- 

 tion. Such complementary hosts should, when practicable, 

 be removed from the immediate vicinity, and when possible, 

 not allowed to exist within considerable distance, one eighth 

 to one half mile, or better still, a greater distance. When 

 it is not practicable to remove the host, the offending por- 

 tions may be cut away, e.g. in the case of the apple rust 

 the cedar balls may be removed from adjacent trees. 



8. Avoidance of disease-bearing material or material 

 favoring disease. — Infection may reach hay through 

 sick melon vines (melon wilt), or manure through sick plant 



