454 



PRACTICAL BOTANY 



415. Checking and removing disease. The prevalence of 

 plant diseases has been made apparent in preceding chapters. 

 Although the nature of many of these diseases is not known, 

 scientific study has contributed methods of prevention, control, 

 or elimination in many cases. Oat smut, which on an average is 

 said to destroy each year from one dollar to five dollars' worth 



FIG. 350. Results of proper pruning and spraying in growing Jonathan 

 apples, Spokane, Washington 



The number and average size of the apples are increased and the quality is 

 improved. Photograph by August Wolf 



of oats per acre, can be removed by application to the seed of 

 a formalin solution at a cost of a few cents per acre. It is not 

 uncommon for the yield of an apple orchard to be doubled by 

 proper spraying, and the accompanying improvement in the 

 quality of the fruit changes it from a, poor quality with a poor 

 market, if it has any at all, to a good quality with good market. 

 A very carefully recorded experiment in the value of con- 

 trolling the disease known as potato blight illustrates the 



