BULLETIN 231] WALNUT CULTURE IN CALIFORNIA. 379 



SEEDLING ROOT ROT WILT. 



Nursery seedlings of the southern California black walnut occa- 

 sionally wilt and die rather suddenly and show, on examination, a 

 black rot of the main root just below ground. This may appear either 

 before or after grafting, and ordinarily, at the worst, picks out only 

 a tree or two here and there, even in a large nursery. We have known 

 of only one case where serious loss was experienced from this source, 

 and this on poorly drained land where the trees were injured by an 

 excess of water. The trouble is caused by a soil fungus, and seems to 

 be confined to the southern California black. 



LITTLE LEAF, "YELLOWS." 



In this disease spindling yellow shoots develop wihch usually die 

 back from the top. All degrees of the trouble may occur from slightly 

 unnatural yellowing and slenderness of the normal shoots to the produc- 

 tion of abnormal clusters of small, yellow, sickly shoots with very slen- 

 der, yellow, poorly developed leaflets. Such shoots in bad cases usually 

 die back at the end of each season. This disease affects the English 

 walnut and is even more pronounced on the northern California black 

 in certain seasons and places. It has been abundant even on black 

 walnut trees of large size in some parts of northern California during 

 the last two or three years and very prevalent in nursery trees of the 

 northern California species grown in the southern part of the State. 

 The southern California black walnut is, so far as our experience goes, 

 immune to this disease, while the Paradox and Royal hybrids, especially 

 the latter, are much less susceptible to it than either the English or 

 northern California black. This disease is not confined to the walnut 

 but is evidently the same as the so-called " Little Leaf" of the grape, 

 peach, apple, quince and umbrella tree z and the mottled leaf of the 

 orange. The "Frizzles" or "Rosette" of the pecan seems also to be 

 of a similar nature. Experience has shown beyond any reasonable 

 doubt that the occurrence of all these troubles has been the result of 

 the abnormally long dry seasons of the past three years. These diseases 

 have occurred particularly, or in fact altogether, on soils where for any 

 reason the subsoil has become very dry during the latter part of the 

 season. Such condition has been most commonly caused by sandy or 

 gravelly subsoil but may also result from the presence of hardpan or 

 a layer of heavy soil within two or three feet of the surface. The con- 

 trol of this trouble lies entirely in irrigation, especially in the late 

 summer and fall during seasons when the rains are late in commencing. 



