280 CULTURE OF IRISH POTATOES 



5. Stem blight, caused by Corticium vagum. 



6. Fusarium wilt, caused by Fusarium oxysporum. 



7. Verticillium, caused by Verticillium albo atrum. 

 C. Affecting the tubers chiefly : 



8. Common scab, caused by Streptothrix scabies. 



9. Powdery scab, caused by Spongospora subterranea. 



10. Wart disease, caused by Chrysophlycetes endobiotica. 



11. Dry rots, caused by several species of Fusarium. 



FIG. 110. In the foreground is a spot where a dozen plants, in a good field, have been 

 killed by the disease rhizoctonia. 



12. Bacterial soft rots, caused by Bacillus solanacearum and 



B. phytophthorus, and other bacteria. 



13. Leak, caused by Rhizopus nigricans. 

 D. Affecting all parts of plants : 



14. Late blight, caused by Phytophthorus infestans. 

 Unfavorable climate, usually hot, dry weather, causes sun scald 



and tip burn. Arsenical poisoning sometimes results from 

 spraying. 



Of the above diseases, the common scab is most abundant, but not 

 very injurious. Late blight is the most destructive disease, and 

 probably black leg is next. 



