POTATO DISEASES IN I907. 32I 



Dr. Jones,* who has made a careful study of this disease as it 

 occurs in Europe, makes the following statement with regard 

 to the causes and treatment : 



"It is not propagated in seed or soil and is non-parasitic. 

 It is considered to be the direct result of malnutrition associated 

 with unfavorable soil conditions, resulting either from too dry 

 conditions or from the lack of potash and lime. It is frequent in 

 light, dry soils, during dry seasons, and is never seen on heavy, 

 strong, moist soils. The remedy, in the judgment of the special- 

 ists cited, lies wholly in attention to cultural conditions and the 

 choice of varieties. 



"Some' varieties are more liable than others to internal brown 

 spot and should not be used on soil that favors the disease; e. g. 

 Mr. Scarlett stated that the British Queen variety is especially 

 predisposed to 'sprain.' The primary remedy, however, lies in 

 the selection and treatment of the soil — i. e., avoiding dry soil — 

 and in so cultivating as to conserve moisture, while using lime 

 and potash liberally." 



From our present knowledge it would seem then that this is 

 not a disease to be feared on soils which are particularly 

 adapted to potato culture and that there is no danger of its 

 spreading like a parasitic disease. It is, therefore, one of the 

 so-called physiological diseases and due to purely local soil 

 conditions. There is some lack of balance in the nutrition of 

 the plant when grown on certain soils which is indicated by 

 the spotting of the tubers. What this is and how to remedy 

 the condition we do not know except as indicated above. 



At our request Mr. Fish planted some of the diseased tubers 

 last spring. Writing on October 29 he states that the plants 

 from these tubers grew as vigorously as any others in the field 

 and produced a good crop of sound potatoes. No brown spots 

 could be found in any of them. 



Surface Spotting op Tubers by Phytophthora infestans. 

 In the early spring of 1907 several growers and shippers 

 called the writer's attention to what they felt sure to be a new 

 potato disease, characterized by a spotting of the surface or 



* Jones, L. R-, Bureau of Plant Industry, Bui. 87, p. 13 (1905). 



