650 INSECTS AFFECTING VEGETATION 



Yellows. -Spindling, yellow shoots develop which usually die 

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

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

 duction of masses of small, yellow shoots, with continual dying back. 

 This affects the English walnut, and is even more pronounced on the 

 Northern California black walnut 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. At the same time and in 

 the same nurseries seedlings of the Southern California black walnut 

 have never shown the slightest indication of this trouble. This dis- 

 ease appears to be the same which affects the peach (which see), and 

 also to some extent the pecan, apple, and many other trees. It is 

 probably due to a climatic or soil condition rather than to any para- 

 site. Conditions which result in sour sap and similar troubles in the 

 stone fruits seem to be related to this disease, and it is very likely 

 due to a disturbance of the dormant or resting condition through 

 which these trees normally pass during the winter. Also seems to 

 be connected with lack of rain or irrigation late in the season. 



Crown Gall Black Knot. Walnut trees are affected in some 

 instances with large knots or cankers on the trunk just below ground 

 or a slight distance above ground. This trouble is not a common 

 one, but seems to occur in some districts more than others. Whether 

 such knots are due to the real crown gall organism (Bacterium tume- 

 faciens) has never been determined, but their appearance leads one 

 to suspect that they originate from infection of scars or wounds on 

 the trunk by this parasite. Known only upon the English walnut. 

 As soon as the trouble appears cut out the diseased tissue, disinfect 

 with strong bluestone solution and paint over the wound. 



Crop Failure. It is a very noticeable fact in connection with 

 the California walnut industry that the total product of the groves 

 of the state is not materially increasing, although the acreage has 

 multiplied many times during recent years. This is due to a very 

 general condition of poor production in the large walnut-growing 

 sections of the southern portion of the state. The older groves, al- 

 though by no means at an age when they should be deteriorating, 

 show very little tendency to increase their yield, and in many cases 

 are gradually going back. The quality and size of the nuts, as well 

 as the quantity, is also a source of complaint. Many of the nuts 

 which mature are empty or poorly filled with shriveled, light weight 

 meat, giving the nut when cracked an unattractive appearance. 

 (Gal. E. S. B. 218.) 



Trouble of this nature is quite commonly attributed to walnut 

 blight, with which disease, however, it has nothing to do. There is 

 probably no one cause or reason for this condition. It is due, gener- 

 ally speaking, to a loss of vitality in the trees, brought about mostly 

 by unavoidable mistakes made in planting when the industry was 

 new and experience in walnut growing very limited. In the first 

 place, all the older groves were planted with the trees too close to- 



