220 The Potato 



mixture, it would indicate that more lime-milk is needed 

 to neutralize the copper sulphate solution. When suffi- 

 cient lime is added, no brown precipitate will be formed 

 by the potassium ferrocyanide solution. Bordeaux mix- 

 ture will burn the foliage of plants if it is not properly 

 neutralized. It is unnecessary to measure the milk-of- 

 lime in making bordeaux mixture if the mixture is tested 

 from time to time with the ferrocyanide solution while 

 adding the lime. The test will indicate when sufficient 

 lime is present. 



When it is necessary to spray with a poison in order 

 to kill potato beetles and other biting insects, the re- 

 quired amount of poison may be added to the bordeaux 

 mixture. 



Other remedies 



Soda bordeaux, in which an equal amount of sal-soda is 

 used in place of lime, has been employed by some potato- 

 growers, but carefully conducted experiments indicate 

 that other preparations with copper compounds are in- 

 ferior to lime. Dry bordeaux applied as a dust has not 

 proved to be a satisfactory fungicide. Lime sulphur solu- 

 tion is also unsatisfactory and unsafe. Where it has 

 been used in experimental work, potato plants sprayed 

 with it have given smaller yields than the unsprayed ones. 

 Powdered sulphur and arsenate of lead or arsenate of zinc 

 have been tried in New Jersey on early potatoes, but have 

 been found to be less satisfactory and more expensive 

 than bordeaux mixture. 



Fusarium dry rot and other rots are caused by organ- 

 isms that gain entrance to the tuber through wounds. 

 Potatoes with tender skin loaded into cars in hot weather 

 soon after digging often rot badly. Care in handling the 



