12 . U. S. DEPARTMENT OF AGRICULTURE. 



turity of the plant, to the acidity of its tissues, or more 

 commonly to some unknown factor in the composition of the 

 protoplasm of the cells themselves. * 



Disease Control. 



By disease control is meant the elimination, the checking, 

 or the prevention of a disease. Plant diseases usually are 

 controlled by prevention rather than cure. A very gener- 

 ally used method in the control of diseases due to parasites 

 is the spraying, dusting, or dipping of plants or plant parts 

 to kill the fungi and bacteria present on the surfaces, or to 

 prevent the germination of spores that may lodge thereon 

 subsequently. There are a number of other practical 

 methods of disease control, such as proper cultural methods, 

 crop rotation, soil and seed sanitation, planting of disease- 

 free stock or disease-resistant varieties, and the variation 

 of the planting date. 



In the control of transportational diseases, icing, refrig- 

 eration, ventilation, precaution not to pack wet plants or 

 plant organs, drying of plants, and careful handling are 

 important means of disease control. 



