188 POTATOES 



tubers should be of large size at this time and further use of the 

 cultivator is apt to disturb them or dig them out of the ground. 



Spraying for Blight and Beetles.---The two worst enemies of 

 the Irish potato crop which can be controlled by spraying are late 

 blight (Fig. 84) and the Colorado potato beetle. The blister 

 beetle and the black flea beetle are sometimes serious pests. These 

 however can be controlled by the same methods as are used for 

 the Colorado potato beetle. 



Spraying with the combined spray will control these enemies 

 fairly well. Bordeaux mixture used before the blight begins will 

 very largely prevent its attacks. Poisons applied when the beetles 



Fig. 84. — Late blight disease of potatoes showing the shrunken, rotted area. Avoid 

 planting affected tubers and spray the growing crop with Bordeaux mixture. (Ohio 

 Station.) 



are at work will kill them. For this purpose arsenate of lead or 

 Paris green may be used. 



A combined spray material is made by mixing arsenate of lead or 

 Paris green with Bordeaux mixture. The amount of poison used 

 with the Bordeaux would be the same as with a like amount of 

 water. (See Chapter XXV.) Make up the desired amount of Bor- 

 deaux mixture and add as much poison to it as if it were merely 

 water. When this combined spray is applied to the potato crop 

 the beetles are killed, better than when the poison is used without 

 the Bordeaux because the spray material is not so easily washed 

 off by rains. The plants are not so likely to be injured by the 

 arsenic in the poison because the lime in the Bordeaux takes up 

 the free arsenic and prevents injury. 



As the plants form new growth another spraying is required to 



