PREVENTION AND CONTROL 269 



and plants selected or seed saved from the healthiest 

 and most desirable plants. Continuation of this 

 method from year to year will in many cases prove 

 extremely helpful in the prevention of some diseases. 

 However, the grower should bear in mind the necessity 

 for selecting plants which possess a combination of 

 desirable characters, characters which give us the 

 desired commercial product as well as characters which 

 give healthy plants. 



Removal of Diseased Individuals. In some cases 

 plant diseases can be held in check by the removal of 

 diseased plants, thus preventing the rapid spreading 

 of the disease. This method is especially useful in 

 orchards, and can also be used to great advantage in 

 combating corn smut and mosaic diseases of tobacco. 

 The diseased plants should be burned, and care should be 

 taken not to bring them in actual contact with healthy 

 plants, since many diseases can be readily transmitted 

 by contact. 



The pruning out and burning of diseased parts of 

 trees is a very successful method of holding certain 

 diseases in check. However, since many organisms of 

 disease will continue to live and produce spores on the 

 part that has been removed, it becomes especially 

 important that these diseased parts should not be 

 thrown on the ground and left unburned, unless the 

 grower is thoroughly familiar with the disease and the 

 organisms that produce it, and knows that these 

 organisms will perish after removal from the host 

 plant. The wounds which are made as a result of this 

 pruning should be painted with white lead, tar, or other 

 antiseptic preparations, to prevent infection by the same 

 or different organisms of disease. In some cases it is 

 also desirable that the workmen's tools should be 

 disinfected. 



Cleaning of Fields. Some organisms of disease 

 persist from year to year on the dead plants and debris 

 of the fields. When a disease of this kind has been 

 very abundant in a field, precaution should be taken 



