FUNGI IMPERFECTI 301 



XIII. EARLY BLIGHT OF THE POTATO 

 Macrosporium Solani E. & M. 



CHESTER, F. D. A Leaf Blight of the Potato. Del. Agl. Exp. Sta. Rept. 4 : 



58-60. 1891. 

 GALLOWAY, B. T. The Macrosporium Potato Disease. Agl. Sci. 7 : 370-382. 



1893. 



JONES, L. R. Potato Blights. Vermont Agl. Exp. Sta. Rept. 9: 66-88. 1895. 

 JONES, L. R. Certain Potato Diseases and their Remedies. Vermont Agl. 



Exp. Sta. Built. 72 : 1-32. 1899. 

 JONES, L. R., and GROUT, A. J. Notes on Two Species of Alternaria. Built. 



Torrey Bot. Club 24: 254-258. 1897. 



STEWART, F. C, EUSTACE, H. J., and SIRRINE, F. A. Potato Spraying Ex- 

 periments in 1906. N. Y. (Geneva) Agl. Exp. Sta. Built. 279: 155-229. 



1906. 

 STURGIS, W. C. Notes on " Early Blight " of Potatoes. Conn. Agl. Exp. Sta. 



Rept. 18 : 127-135. 1894. 



Habitat relations. The fungus causing the early blight of 

 potatoes was described in 1882. In 1891 it was recorded as of 

 economic importance in the United States, but subject to control. 

 Since that time this fungous disease has grown constantly in im- 

 portance, although to a very large extent preventable. The early 

 blight is common practically throughout the United States, and 

 it occurs also in Canada, Europe, Asia, and Australia. 



In temperate regions the leaf blight may be found from July to 

 the end of the growing season, increasing generally as the season 

 advances. It may be checked, however, by periods of unusual 

 drought, but it does not appear to be easily affected by lesser 

 changes in conditions. 



This disease is a typical leaf blight and may be distinguished 

 from the late blight already described and from such nonparasitic 

 pathological conditions as tip burns and sunscald by recognizable 

 leaf characters. The spots are brown, circular, or elliptical, and 

 they are distinctly marked with concentric or target-board mark- 

 ings. They are irregularly distributed over the leaf surface, al- 

 though frequently occurring upon the borders of other injuries 

 (Fig. 136). Through carefully conducted experiments (Jones) it 

 has been satisfactorily determined that the fungus may establish 

 itself by truly parasitic means, being capable of infecting healthy 

 leaves, provided only that sufficient moisture is present to insure 

 germination and vigorous growth. Nevertheless, the fungus is 



