Diseases of the Potato 189 



Early blight (Plate X) 



Early blight, caused by the fungus Altemaria solani, 

 appears as angular, dark brown dead spots on the leaves, 

 which may become so numerous as to kill the entire leaf. 

 The spots are marked with concentric rings of elevation, 

 gi\Tng the dead area a target-board appearanc-e. The 

 \Tnes usually do not become affected until after blossom- 

 ing has occurred, but may then become so severe as to 

 cause the ^"ines to die. The spots often occur around a 

 flea-beetle puncture or other injury', but may also be 

 foimd on an otherwise iminjiu-ed surface. The fimgus 

 commonly attacks the older and weaker leaves first, but 

 may spread from them to the younger ones. 



The disease may be confused with tip-bum or with 

 arsenical or other injury" to the foHage. The fungus 

 may attack such injured or dead area first and later 

 spread to healthy tissue. The spores are large, thick- 

 walled, many-celled bodies produced on both surfaces of 

 the older dead areas. The fimgus is able to hve over 

 winter as a myceliiun in the dead leaf tissue, and the spores 

 themselves will remain ahve for more than a year. They 

 germinate in water, each cell being capable of sending 

 out a germ-tube. These are able to enter the leaf through 

 stomates or penetrate the epidermis directly. The 

 fungus attacks the fohage only, but as a result of the 

 attack the tubers may be small and thus the loss will be 

 considerable. This will depend upon the virulence of 

 the attack and may amoimt to one-half or more of the 

 crop. 



The disease can be held in check by thorough appli- 

 cations of bordeaux mixtiue. 



