152 Report of the Botanist of the 



If, in the J agger experiment, we subtract from the total expense 

 of the spraying, $50.91, the amount of the probable expense neces- 

 sary to control " bugs; " namely, $18.90, there is left $32.01 which 

 is the actual extra expense of using bordeaux 4 times. Now, if we 

 divide the total net profit, $300.09 by $32.01 we get as a quotient 

 9+ which is the number of years Mr. Jagger can spray the same area 

 in potatoes without incurring loss even though no increase in yield 

 is obtained during that time. 



In the same manner it can be shown that in the Salisbury experi- 

 ment No. I enough clear money was made to insure against loss dur- 

 ing the next 7+ years ; in the Salisbury experiment No. 2, 7+ years ; in 

 the next 7+ years ; in the Salisbury experiment No. 2, 7+ years ; in 

 the Welch experiment, 8+ years; and in the Martin experiment, 6+ 

 years. 



CAUSES OF FAILURE. 



Because of the heavy loss from blight in 1902 an unusually large 

 number of farmers sprayed their potatoes in 1903. Some were suc- 

 cessful while others failed. Naturally, those who failed wish to 

 know why they failed in order that they may be more successful 

 another season. No doubt many are discouraged and have reached 

 the conclusion that potato spraying is a failure. 



There are two common causes of failure : (i) The spraying is not 

 done at the proper time; or (2) it is not done thoroughly. During 

 the past season the blight appeared so suddenly that many were taken 

 unawares and, before they could spray, the plants had already become 

 infected. Some made one or two applications in July when bugs 

 were prevalent and then neglected further spraying until the blight 

 appeared during the last week in August. In most cases where this 

 was done there appeared to be- but little benefit from the spraying. 



An interesting example came under our own observation. Two 

 small fields of potatoes on the Station farm were sprayed twice early 

 in the season with bordeaux and paris green and then neglected until 



