42 MAINE AGRICULTURAL EXPERIMENT STATION. 



erable size and the weather conditions are favorable.- The 

 fungus causing the disease is very sensitive to high temperature. 

 Exposure for any considerable period of time to a temperature 

 of 90% to 95% F. or over kills it while continuous and pro- 

 longed exposure to a temperature above 86% or 87% F. will 

 accomplish the same results. 



The month of July in both 191 1 and 1912 was characterized 

 by a period of about 10 days, at the beginning, of the most 

 severe and continuous hot weather recorded in Maine in many 

 years. Not only were high temperatures recorded but the 

 days were very bright and sunny and the nights abnormally 

 warm. During this period young apples on the exposed portions 

 of the trees were partially cooked on one side as a result of the 

 extreme brightness and heat of the sunlight. It seems quite 

 possible that the air and soil temperature were so high that the 

 late blight fungus was in many instances practically killed out 

 during this period. Moreover it came at a time when the 

 fungus was probably no longer alive in the seed tubers but 

 existed in a vegetative stage in the young stems and leaves 

 above or at least very close to the surface of the soil, if below 

 the ground at all. 



The hot period of July 1911 was followed by a fairly dry 

 season and there resulted the most healthy crop of potatoes, so 

 far as late blight was concerned, that Maine has produced in 

 years. Consequently the seed tubers used in 1912 contained 

 very little of this disease. The only dry period of the growing 

 season of 1912 was the month of June. This was followed by 

 the hot period of July, already referred to, and apparently fur- 

 nished the final causes which nearly eliminated late blight from 

 the State this year. 



Early blight normally does little damage in wet seasons, but 

 some cases were observed this season where, associated with 

 flea beetles it caused considerable damage. Blackleg and scab 

 caused about the usual amount of losses. The wet weather 

 was quite favorable to the development of the former. Very 

 favorable reports were received from those who used the for- 

 maldehyde seed-treatment for these diseases. 



