THE POTATO 179 



duction, however, seems to be hastened and 

 enormously increased when a few days of warm, 

 cloudy and muggy weather alternate with the 

 longer, cooler periods. Under such conditions a 

 field showing but slight infection may in a few 

 days look as if it had been swept by fire or frost. 

 It rarely attacks early potatoes, mostly appearing 

 upon the late varieties during the tuber-forming 

 period. 



"Various experiment station workers have tried 

 different remedies for holding this disease in check. 

 At some stations these experiments have been 

 carried on for many years. While several have 

 given results which were of value, no treatment 

 has been as uniformly successful as the application 

 of Bordeaux mixture. The universal experience 

 is that spraying with this fluid will so nearly con- 

 trol the late bhght as to make it possible to secure 

 a crop even in those years when this disease is 

 most prevalent. It requires, however, that the 

 spraying should be begun in time and continued 

 at intervals throughout the growing season. As 

 already stated, it must be a precautionary measure. 

 If not begun until after the blight is evident in the 

 field only partial control can be expected. If the 

 spray is applied thoroughly from the beginning, 

 not only will the blight be controlled, but the rot 

 of the crop which usually follows a severe attack is 

 altogether prevented. 



'*It has been almost conclusively proved that the 

 rot of the tuber which follows an attack of late 

 blight is really due to the infection of the tuber by 

 the spores which have fallen upon the soil and 

 which, in the course of the season, are carried by 

 rains or irrigation waters into contact with the 

 tuber itself. Here it may begin growth at once or 



