OBSERVATIUNS UN THE POTATO DISEASE CONDITIONS IN 



MICHIGAN FOR THE SUMMER OF l!tlS. 



E. F. Wooucoc!K. 



The results included in this paper were ohtuined in connection with survey 

 work carried out during the summer of 1918 under the supervision of the 

 Plant Disease Survey of the United States Department of Agriculture The 

 primary object of the survey was to locate Late Blight if it should appear in 

 the state, and take measures to prevent the spread of the disease. In connec- 

 tion with the survey for this partciular disease, which was not found in tlie 

 state, the potato diseases discussed below were observed. 



TIP BURN. 



The injury done by this trouble consisted of the destnictiou of leaf area 

 at a time when the plant was manufacturing food for storage! in the develop- 

 ing tubers. As a result of this the yield, especially in the early varieties, was 

 cut down fully 50% in severe cases. Ninety per cent of the counties visited 

 in the lower peninsula showed the trouble, while only 64% of the counties in 

 the upper peninsula were affected. This difference in percentage of distri- 

 bution throughout the state is due to the fact that most of the lower peninsula 

 suffered from a severe drought during the growing season, while the upper 

 peninsula received sufficient rainfall. The work of E. D. Ball,* suggesting 

 a relation between leaf hoppers and the tip burn, had not come under my 

 observation, so that no complete notes were taken relative to their presence 

 throughout the state. 



The percentage of injury in llie following table sunnna rising my ohscr 

 vations on Tip Btu'ii has reference to Ihe amounl of leaf area killeil : 



SUMMARY TABLE No. 1 



RHIZOCTONTA (CORTICIUM VAGUM VAR. SOLANl) . 



The disease was found in 42% of the fields visited and quite generally 

 distributed. In the early part of the season its presence was evident by the 

 stunting effect on the developing tops. One lielil in Oakland county showe<l 



♦Ball, E. D. Science 48: 194. 

 to the Leaf Hopper. 



21st Mich. Acad. Sci. Kept., 1919 



1918. Leaf Burn of the Potato ami its liclativn 



