378 Report of the Mycologist op the 



ment has sometimes saved almost an entire crop at an expense of 

 i wo or three dollars per acre, which shows that, at times, spray- 

 ing is exceedingly profitable. It is quite generally conceded that 

 it will pay to spray potatoes in those seasons in which late blight 

 occurs. 



The late blight, however, does not occur every season. In 

 some portions of the United States it never occurs. On Long 

 Island it probably occurs destructively about one year in four, on 

 the average. Now, spraying is preventive, not curative, and so 

 nmst be commenced before it is known whether the disease will 

 appear. According]}^, farmers have come to look upon spraying 

 as a form of insurance, and some have raised the question, " Can 

 we not better afford to lose a crop occasionally than to bear the 

 expense of spraying every season?" Those who ask this ques- 

 tion assume that spraying is of no value except to prevent the 

 late blight. But that is not true; spraying benefits the potato 

 plant in other ways : 



(1) Spraying protects it against the attacks of early blight 

 (Macrosporiujn solani), a disease which attacks the leaves, pro- 

 ducing circular or elliptical, dead, brittle spots which are marked 

 with dark colored rings arranged concentrically, like the rings on 

 the ball of the thumb. This disease is not as conspicuous as the 

 late blight but, on the whole, is perhaps fully as destructive since 

 it is more widely distributed and occurs to some extent every 

 season. 



(2) Spraying, if done thoroughly, will prevent the greater 

 part 01 the damage done by flea-beetles {Crcpidodera [Epitriiv] 

 cucumeris). 



(3) The plants can be more completely protected against the 

 attacks of Colorado potato-beetles (Doryphora decemlineata), than 

 is possible by any method in which Paris green is used alone. 



(4) The danger of injury to the foliage from Paris green 

 poisoning is avoided. 



(5) Some of the best authorities on the spraying of plants hold 

 that Bordeaux mixture has a beneficial influence on potato foli- 

 age even when no insects or diseases are present. The nature of 

 this influence has not yet been satisfactorily explained. 



