328 Journal of Agricultural Research voi. xiir. no. 6 



4 — 



occur. It has been observed the first year in newly seeded fields in 

 close proximity to old fields where the disease occurs. Thus, there is 

 no evidence either from the study thus far made of the life history of 

 the fungus or from field observation that indicates that the disease is 

 carried by properly cleaned seed. But it does appear likely that the 

 ascospores are blown at least short distances by the wind. It is also 

 clearly evident that any infected alfalfa hay or debris might easily con- 

 vey apothecia which would become a source of infection under suitable 

 conditions. 



CONTROL MEASURES 



No experiments have been conducted to determine the efficiency of 

 possible control measures. If, as now appears, the only source of infec- 

 tion is the ascospores, cutting the alfalfa before these are mature should 

 greatly reduce the disease. In fact, ,so far as the writer has observed, 

 this is the case. In fields which make a vigorous growth during the 

 entire season and which are cut for hay at the stage usually recom- 

 mended, this leafblotch is never important. But if for any reason an 

 infected field is allowed to remain uncut for an unusually long period, 

 especially in the cool, moist weather of spring and autumn, the disease 

 becomes abundant and destructive, provided a source of infection is 

 present. Lodged plants which have escaped cutting, or plants left 

 standing in fence corners, may become important sources of infection at 

 this time. Uncut plants of this character also provide excellent facilities 

 for the overwintering of this fungus, as well as several others, and should 

 be carefully eliminated wherever the disease is troublesome. 



SUMMARY 



(i) The disease of alfalfa here described as the yellow-leaf blotch is 

 one of considerable economic importance which has been recognized in 

 America only during the last three years (1915-1917), although it has 

 long been known in Europe. 



(2) The yellow-leaf blotch occurs in important alfalfa-growing regions 

 from New Jersey to Oregon, and at least as far south as Teimessee. 



(3) The injury is brought about, either directly by a slow killing of 

 the infected leaves, or indirectly by furnishing easy access to the weakened 

 leaves for other organisms. 



(4) The causal organism (Pyrenopcziza medicaginis) is a fungus which 

 produces, first, a conidial stage on the living leaves and later, ascigerous 

 stages on the portion of the leaf which has been killed. 



(5) The fungus has been grown in culture, where both the conidial 

 and ascigerous stages have been produced. 



(6) Infection appears to take place only from ascospores, which upon 

 germination are able to penetrate the epidermal cells of the leaf. The 

 viability of the conidia has not been conclusively demonstrated. 



