June 3, 1918 Blackleg of Potato and Temperature and Precipitatian 509 



The experiment at Norfolk also seems to indicate that the organism 

 does not overwinter in the soil, even under climatic conditions much 

 milder than those found in Maine. 



BLACKLEG AS FOUND IN NORTHERN MAINE IN 1914, 1915. AND 1916 



During the summer of 191 4, following a winter with an average mean 

 minimum temperature of 8.06° F., an average mean maximum of 30.58°, 

 and an average monthly precipitation of 2.72 inches, the blackleg was 

 very prevalent in the potato fields under observation in Aroostook 

 County. It was then attributed to a variety of conditions. However, 

 no actual counts showing the percentage of the disease were made. The 

 following year (191 5) blackleg was likewise very prevalent in the same 

 and other fields. This was also true in commercial fields where disin- 

 fection but not careful selection of the seed was practiced. The Irish 

 Cobbler and Spaulding Rose were attacked as severely as any of the 

 other varieties. For this reason the observations recorded here for 

 1 91 5 and 1 91 6 have been made on these two varieties. During these 

 two summers a number of fields were inspected, and counts made as 

 to the percentage of infected plants. As far as possible, counts were 

 made on the same fields in 1915 and 1916. In all cases the seed used 

 in 1 91 6 was the progeny of the fields from which the counts were made 

 in 191 5. The results are presented in Table II. The significant thing 

 about the results is the great difference in the percentage of blackleg 

 found during 191 5 and 191 6. There is a striking uniformity in regard 

 to this difference in six different fields from two varieties, an early and 

 a late one. The counts were made approximately on the same date in 

 both summers, and as far as possible, the same treatment and cultural 

 conditions were employed both seasons. By examining the percent- 

 ages of disease in the totals as given in Table II for the Spaulding Rose, 

 it will be seen that in 191 5 the percentage of blackleg is 8.47, 7.52, and 



