THE DISEASES OF PLANTS 



diseased field. 

 is done. 



Figs. 99 and 100 show how the spraying 



EXERCISE 



Watch the potatoes at the next harvest and estimate the number 

 that is damaged by scab. You will remember that formalin is the 

 substance used to prevent grain smuts. Write to your State Experi- 

 ment Station for a bulletin telling how to use formalin, as well as for 



FIG. 100. SPRAYING MACHINE 



information regarding other potato diseases. Give the treatment a 

 fair trial in a portion of your field this year, and watch carefully for 

 results. Make an estimate of the cost of treatment and of the profits. 

 How does the scab injure the value of the potato ? The late blight 

 can often be recognized by its odor. Did you ever smell it as you 

 passed an affected field ? 



