EXPERIMENT STATION BULLETINS. 



647 



Fig. 1. Potato leaf showing hopperburn. Note the burned effect of tips and margins of leaflets, also the tendency to curl upward 



reported to the Plant Disease Survey- from various states. The total 

 loss to the United States potato crop in that season was 3.7 per cent 

 or 1(5,348,000 busliels. Tlie loss to Michigan growers was estimated at 

 25 per cent or 10,240,000 bushels. 



THEORIES AS TO THE CAUSE OF "^^Tn'RURN'^ 



Dry Weather: In 1895 Jones-^ offered a plausible explanation of "tip- 

 burn." In contrast to late and early blights, which are of fungous origin, 

 lie thought that "tipburn" was "attributable to the unfavorable conditions 

 surrounding the plant, especially dry hot weather, with insufficient 

 water supply." For want of a more satisfactory one this explanation 

 of tipburn has been quoted in practically all potato disease handbooks 

 published since that time. 



Lutman* in 11)11) jjublislied data supporting the dry weather theory, 

 in which he states "TipbiH'n of the potato is due to excessive heat and 

 sunshine during late July and early August. An inordinate transpira- 

 tion from portions of the leaflets directly affected results in a wilting 

 from which the parts seriously injured do not recover." 



It has been repeatedly shown since Golf's^ trials in 1891 that potatoes 

 sprayed with bordeaux mixture have been comparatively free from 

 "tipburn" injury. There is then a contradiction in the observed facts 



