322 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION. 



were made from these diseased scions, but from the limited material at 

 hand no true walnut blight organism was isolated. These scions were 

 grafted into black walnut trees and in the new growth from some of 

 the scions typical walnut bacteriosis appeared close to the old wood of 

 the scion, although there was no walnut blight in the vicinity, local 

 scions did not develop the disease, and on the shoots from the French 

 scions blight developed only close down to the original imported wood. 

 While the evidence seems to indicate that this disease may have been 

 introduced from France, we have found no report of its occurrence in 

 that country in available literature. It may, however, be confused with 

 their Marsonia, and really occur there to a limited extent. 



History of Disease in California. The disease has been known for a 

 considerable time in California. The first published account which we 

 have found occurs in the report of the Secretary of Agriculture for 

 1893.* At that time the true cause of the trouble had not been demon- 

 strated, although the presence of a bacterial organism had been found 

 constantly associated with the disease, and pure cultures of an organism 

 had been made by Professor Newton B. Pierce, who was then in charge 

 of the Pacific Coast Laboratory of the Division of Vegetable Physiology 

 and Pathology of the United States Department of Agriculture. 



Growers affirm that the trouble had been known for several years 

 before this time. According to local accounts, it appears that the dis- 

 ease first became noticeable in the principal walnut districts of Los 

 Angeles County about 1891. The disease occurred then in a very limited 

 way and seems to have attracted attention, not on account of the extent 

 of its ravages, but simply from the fact that it was something new. 

 Growers who observed the blight at that time claim that its occurrence 

 coincided with the distribution of trees from a certain nursery in Orange 

 County, the proprietor of which nursery imported walnut trees from 

 France a few years previous. Whether or no these statements are cor- 

 rect, it appears to be undoubtedly true that the blight was first noticed 

 in Los Angeles County about 1891, that it came thence from Orange 

 County, and that the disease then spread northward to Ventura and 

 Santa Barbara counties until at present it occurs in practically all parts 

 of the State where walnut trees exist. 



Walnut bacteriosis is by far the most prevalent in the older walnut 

 sections. Some differences as to amount and severity can, of course, be 

 noted in different places, due either to different climatic conditions or 

 to the fact that the disease has not yet been introduced. The newer 

 groves that are now being grown in central and northern California are 



*Report of Secretary of Agriculture, Division of Vegetable Pathology, 1893, p. 273. 



