A S.udy of Meadow-Crop Diseases in New York 53 



CERCOSPORA LEAF SPOT 



Suscepts 



The writer (1929) has shown that red, zigzag, alsike, white, sweet, and 

 hop clovers, yellow trefoil, and alfalfa are affected with Cercospora leaf 

 spot in New York. Records of the following additional suscepts are 

 recorded in the literature: Trifolium al pest re (Saccardo, 1882:556), 

 T. incarnatum (Chester, 1890:96), T. rubrum (Passerini, 1877:124), 

 Medieago arabica (Ranojevic, 1914:420), M. denticulata (Ellis and Ever- 

 hart, 1891), and M. hispida (Wolf, 1916:301). 



The disease 

 History and range 



This disease is widely distributed in the United States. It was first 

 reported from New York by Peck in 1883. It is also recorded from New 

 Jersey (Ellis and Everhart, 1888:7), Delaware (Chester, 1890:96), Ala- 

 bama, Iowa, and Texas (Ellis and Everhart, 1891:89), Mississippi (Tracy 

 and Earle, 1895b: 119), Indiana and Michigan (Stakman, 1922:248), 

 Georgia (Haskell, 1926:366), Missouri and Kansas (Kirby and Archer, 

 1927:197), Utah (Haskell, 1928), and North Carolina (Wolf and Lehman, 

 1924). The European distribution is indicated by records from Servia 

 (Ranojevic, 1914:420), Itftly (Passerini, 1877:124), Austria (Magnus, 

 1905:558), and Hungary (Penzes, 1927). There is no record of its occur- 

 rence in Asia, Africa, or Australia. 



Symptomatology 



The lesions produced by Cercospora leaf spot arc almost without excep- 

 tion somewhat angular and more or less delimited by the veins of the leaf. 



The spots on red clover (figure 10, A) and on hop clover are linear and 

 sharply delimited. Terminal lesions on the leaflets are triangular, being 

 limited on either side by veins from the midrib. Sometimes lesions occur 

 on the pulvini of the leaflets, causing them to yellow and fall. 



The elongated spots on red clover are in contrast with the almost circular 

 spots on sweet clover, and almost all intergrading conditions are found on 

 the other suscepts. Lesions on sweet clover may be 5 millimeters in 

 diameter. As a rule, alfalfa bears spots of the same general shape as those 

 on sweet clover but smaller in size. In the spring of 1928 near Cairo, 

 Greene County, New York, secondary shoots of alfalfa developing under 

 moist conditions before the first crop was cut showed elongated lesions 

 precisely like those illustrated on red clover. It appears then that atmos- 

 pheric conditions and the type of tissue influence the shape of the spot. 

 Alsike, white clover, and yellow trefoil have spots intermediate in shape 

 between the circular ones on sweet clover and the linear ones on red clover. 



