CHAPTEft VII 



POTATOES 



Late Blight and Rot. This disease is responsible for 

 greater losses in potato growing than any other disease, 

 the annual loss in the United States being estimated as 

 $36,000,000. It is more strictly a northern disease, which 

 is supposed to have originated in South America. It has 

 been reported from Ecuador, Italy, Florida, India, and 

 New Zealand, all of which are in or near the tropics. 

 There is no reason why it should not become serious 

 within the tropics, especially in the more elevated places 

 at any time. It is this possibility of its occurrence that 

 leads the author to give this discussion. 



This disease is most destructive in damp rather cold 

 weather. The presence of the disease is indicated by a 

 tendency to wilt quickly, followed by the occurrence of 

 dark spots, which usually start near the edge or tip of 

 the leaf and gradually spread over its entire surface. 

 If the weather is damp the spots are purplish, water- 

 soaked in appearance, and the disease spreads rapidly. 

 If the weather is dry the spots are brown and the 

 disease spreads slowly. Under favourable conditions 

 the disease spreads so rapidly that a promising crop 

 will be entirely destroyed within a very few days. 

 When the disease is active it can be readily recognised 

 by a characteristic vile odour. This disease also attacks 

 the tubers, causing the dry rot, which is very destructive 

 in storage. Not only does the dry rot cause heavy 

 losses, but it makes favourable conditions for infection 

 by the wet-rot bacterium. This disease is caused by 



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