POTATOES 191 



placed over this, the object being to keep the frost 

 in as long as possible. 



Controlling Potato Pests. — Late leaf blight is by 

 far the most destructive, persistent and trouble- 

 some disease that affects potatoes. It is caused by 

 a fungus which, under favorable conditions, ap- 

 pears as a delicate white mildew, hence the name 

 sometimes applied, downy mildew. In some sea- 

 sons it works so rapidly as to completely destroy 

 the foliage of an entire crop within a few days of 

 its first appearance. It attacks the leaves and stems 

 and frequently extends to the tubers, the rotting of 

 whic) "allows quickly upon the decay of the tops. 

 The decay in the tubers is not always proportionate 

 to the decay in the vines, but the relation between 

 these is usually close, hence the wisdom of promptly 

 applying remedial and even preventive measures. 

 The treatment is the same in kind as for early blight, 

 that is, spraying with bordeaux. As the beetles 

 come at the same time as blight, a properly prepared 

 spray will answer for both. 



Little good will result from spraying after injury 

 from the disease has become in any considerable 

 degree apparent. Spraying should begin, there- 

 fore, even before the blight has appeared and 

 usually as soon as the plants are 6 to 10 inches 

 high. The number of sprayings will run all the 

 way from one to six or seven, according to the 

 conditions, especially those that relate to weather. 

 Ordinarily from three to four careful sprayings will 

 suffice, but not in all instances. When but three 

 are given, the first should be deferred until there 

 is danger of harm from the flea or the Colorado 

 beetle. Ordinarily from 10 to 15 days are allowed 

 to elapse between the sprayings, but, in some in- 



