216 The Potato 



pump of the machine should be capable of maintaining a 

 uniformly high pressure. These are factors that must be 

 considered in buying or constructing a machine. Other 

 points are of secondary importance. For small fields of 

 an acre or less, a small compressed air spray may be used. 



The operator should see that the mixture gets on to the 

 vines. It is of little value applied to the soil. It occa- 

 sionally happens that a nozzle becomes clogged, and the 

 vines below are not being properly sprayed. One cannot 

 hope to spray a field adequately by merely driving through 

 it. Much depends on the interest taken by the driver. 

 One can best determine whether the application is thorough 

 by examining the vines after spraying them. 



Various strengths of bordeaux mixture have been 

 recommended. The 5 : 5 : 50 formula is commonly used 

 on potatoes. Experiments have shown that the spores 

 of the blight fungus can be prevented from germinating 

 at a much weaker strength, so that there is little doubt 

 that the blight can be controlled with bordeaux mixture 

 at 2 : 2 : 50 or 3 : 3 : 50. ^Vhen copper sulphate is very 

 expensive, as at present, larger profit can doubtless be 

 secured with a weaker mixture than with a stronger one, 

 which may give slightly increased yields from greater 

 stimulation. 



For many years potato spraying experiments ha\e 

 been conducted in several states. The bordeaux mix- 

 ture has been prepared in various ways, and used at 

 different strengths. The experiments have been con- 

 ducted on experiment station grounds and on farms in 

 ^•a^ious parts of the country. These applications have 

 been made by scientific men and by farmers with hand 

 machines and with traction sprayers. The conclusion in 

 nearly every case has been that it pays to spray with 



