1911.] PUBLIC DOCUMENT — No. 31. 147 



plants for the late spring crop. Careful examination, however, 

 failed to reveal any indications of this disease on the young 

 ]»lants. As has been suggested, this fact seems to indicate that 

 ihe causal organism is not a true parasite, and that it cannot 

 iufcct healthy, vigorous jdants. being more probably one that 

 is ca])al)le of infecting its host only after the latter has become 

 weakened by adverse climatic conditions, or injuries produced 

 by other causes. 



Further observations upon this interesting phase unfortu- 

 nately could not be made, but in a recent text-book on the " Dis- 

 eases of Economic Plants" ^ the following statement is found: 



" The disease does not seem capable of attacking healthy, vig- 

 orous plants, but usually follows injuries produced by other 

 agencies." 



The first indications of the presence of the disease are sub- 

 circular areas of dead tissue from % to Vj, of an inch in diam- 

 cler and brownish in color. (See cut.) These spots soon 

 become more noticeable by the development of a greenish-black 

 felt of fungous mycelium, 1)earing conidiophores and conidia, 

 (Ui l)oth the upper and lower sides of the leaf. The spots are 

 frequently more numerous toward the apex of the leaf, and by 

 the time the fungus felt is well developed, the intervening leaf 

 tissue is yellowed and presents a sickly appearance. Often the 

 leaf is so badly infected that the diseased areas coalesce, leav- 

 ing very little of the leaf tissue visible. 



The market value of the crop is lessened if the leaves are 

 at all spotted, and when badly diseased it is not salable. Even 

 if the whole plant does not collapse from the effects of the 

 fungus, it is greatly injured, and trimming off" the injured 

 leaves necessitates extra labor and expense at harvest time. 



Since the disease is new to this locality, and there ha^■e been 

 M'.ch limited opportunities to study it and the factors responsible 

 for it, it is impracticable to offer any remedies at present. If 

 the disease is sporadic, and caused by adverse conditions, the 

 proper remedy- would be to find out what those conditions ar(> 

 and remedy them. On general lines, however, it would be well 



> Reed, in Stevens & Hall's" Diseases of Economic Plants, — Heterosporiose," p. 288, 1910. 



