REPORT OF THE SOCIETY 87 



will be abstricted. Not many are needed to initiate the outbreak. A coni- 

 diiim germinates in a short time in a thin layer of water on the leaf giving rise 

 to 8 zoospores. These are motile for perhaps an hour, then they come to rest, 

 germinate by a germ tube and infect the leaf. Under moist summer conditions 

 this is repeated approximately in 10 days, but the period elapsing between 

 successive sporulations increases with decreasing humidity. 



Tuber Infection 



Some spores are washed through interstices of the soil to the tubers in the 

 upper part of the hill, and if the skin of the potato is still immature, infection may 

 easily occur. Early infection may cause total rotting of the tuber, while later 

 infection may only give rise to small lesions. It is most important to remember 

 that late attacks of blight will mean a plentiful supply of conidia on surface soil 

 and plant parts at digging time and most tuber infection occurs at this stage. 



Control Measures 



1. Selection of sound seed tubers. 



2. Thorough spraying with Bordeaux from July to mid-September. 



3. Hilling of potatoes to protect upper potatoes in hills from tuber infection. 



4. Removal of tops two weeks before harvesting to prevent tuber infection. 



GROUP 5 

 Disease Caused by an Ascomycete — Wilt and Stem-Rot or Stalk Disease 



Sclerotial diseases of the potato have been reported from many countries 

 within recent j^ears. That known as "stalk disease" caused by Sderotinia 

 Sclerotiorum is common in the West of Ireland and in the northern damper 

 parts of England and Scotland. Growers believe that it is the most serious 

 potato disease in these districts next to Late Blight. A similar disease caused 

 by the same fungus attacks tomato, artichoke, sunflower, bean, squash, cu- 

 cumber, carrot and turnips (Cotton, A.D.) in Great Britain. Bisby has reported 

 a sclerotial disease of sunflower from Manitoba which is common also in Quebec 

 and elsewhere. Mac-Alpine found a sclerotial disease of potato in Australia, 

 which he attributed to S. sclerotiorum, Carpenter one in Hawaii caused by S. 

 Rolfsii, and Pole Evans reports one from South Africa. During the summer 

 of 1921 Mr. O. W. Lachaine found 10 per cent infection of a 4 acre field of 

 potatoes in Restigouche County, New Brunswick, and four other fields of 3 

 or 4 acres had from 1 per cent to 2 per cent infection. The photograph (Fig. 



