272 THE PEANUT— THE UNPREDICTABLE LEGUME 



tention than any other disease of peanuts in the United States, there is 

 Httle agreement as to its relative destructiveness. 



Obviously the defoliation greatly decreases the value of the vines for 

 hay, but as indicated by Miller (94) there are observers who feel that 

 leafspot does not result in appreciable reduction in yield of nuts. The 

 majority of observers, however, maintain that considerable loss in yield 

 of nuts results from the disease. 



The best estimate of importance of peanut leafspot may be obtained 

 from results of studies on control. In Virginia 30 tests showed average 

 yields about 500 pounds per acre less in untreated fields than in fields in 

 which leafspot had been decreased by control measures (94). This indi- 

 cated a loss in yield of about 20 percent from leaf-spot infection. Interpret- 

 ing results of extensive tests in Georgia similarly (172) the nut-yield 

 loss from leafspot is indicated as from 20 to 25 percent. 



Description. Two fairly distinct types of necrotic spotting are recog- 

 nized as common on peanuts in the southeastern United States, and each 

 has been connected with a specific Cercospora sp. (68, 171). The exist- 

 ence of two species of Cercospora associated with peanut leafspot was 

 clarified by Woodroof in 1932 (171). The eflfects produced by these 

 organisms, however, are still regarded as only one disease. Control 

 measures seem equally effective on both organisms. Peanut-breeding 

 programs, however, may produce varieties resistant to only one of the 

 pathogens (61), in which case it may be necessary to divide "peanut 

 leafspot" into two diseases. 



Spotting associated with Cercospora arachidicola Hori {Mycosphae- 

 rella arachidicola Jenkins) appears earlier and becomes epiphytotic 

 earlier than does that associated with C. personata (B. and C.) E. and 

 E. {M. berkeleyii Jenkins). It seems logical, therefore, to designate them 

 "early leafspot" and "late leafspot." There is a period of overlapping, 

 however, and frequently both types of spotting are found on the same 

 plant (171). 



In the initial stages the two types of spotting are indistinguishable 

 (68). Spots appear as slightly pale or blanched-like areas and a break- 

 down of the lower epidermis is evident. The spots develop rapidly and 

 become distinctly yellow on the upper surface of the leaflet. With this a 

 necrosis develops from the center of the lesion, or the entire lesion may 

 become necrotic at one time. 



Later stages in necrosis serve to distinguish between the two leaf- 

 spots (68). Early leafspot is characterized by a yellow halo of variable 

 width, while halos are found only with more mature spots of the late type. 



