246 Report of the Botanical Department of the 



enough to secure the maximum net profit. In order to get some 

 information on this point arrangements were made with several 

 of the experimenters to double-spray a few rows at each spraying. 

 In some cases a strip on either side of the check was double- 

 sprayed ; in others, double-spraying was done on only one side of 

 the check. The double-spraying consisted simply in going over 

 a few rows a second time on the date of each spraying. In com- 

 puting the net profit from double-spraying it has been assumed 

 that the expense of double-spraying is exactly double that of 

 single-spraying. 



Five such experiments were made in 1910 and ten in 1911. 

 The results of the former were published in Bulletin 338 and of 

 the latter in this bulletin, but in order that they mav be more 

 readily comprehended they have I)een tabulated in the accom- 

 panying table. The first five experiments given in the table are 

 those made in 1910; the others were made in 1911. Under the 

 heading " Increase or decrease in yield " there are three columns. 

 The first of these relates to single-spraying, the second to double- 

 spraying while the third shows how much doubling the spraying 

 increased the yield over single-spraying. A minus sign indicates 

 a decrease in yield. 



The figures given in the last column under " Pi'ofit or loss; '' 

 show how doubling the spraying affected the net profit as com- 

 pared with single-spraying. It will be observed that double- 

 spraying proved profitable in eleven cases and unprofitable in the 

 other four, the average result being a net profit of $4.44 per acre. 

 The average increase in yield was increased from 20.2 bu. for 

 single-spraying to 34.7 bu. per acre for double-spraying. 



Considering that these results were obtained in dry seasons 

 when spraying was less profitable than usual the showing made 

 by double-spraying is highly creditable. The writers are con- 

 vinced that most potato growers will find it to their advantage to 

 spray more thoroughly than they have been doing in the past. 



