WALNUT DISEASES 



2011 



Walnut Spraying 



Experiments in spraying walnuts have 

 been carried on by. the United States De- 

 partment of Agriculture, by the Univer- 

 sity of California,* and by a number of 

 walnut growers. Bordeaux mixture 5-5-50 

 and lime-sulphur, as well as other sprays, 

 have been used. The conclusions from the 

 work thus far done are as follows: (1) 

 There are undoubtedly some beneficial 

 effects on the tree from Bordeaux and 

 lime-sulphur sprays, especially in the con- 

 trol of the aphis by the latter spray, and 

 of various fungi. (2) The cost in mate- 

 rials and time is rather large, being from 

 30 cents to $1 per tree, according to size, 

 thoroughness of application, and equip- 

 ment. (3) The thorough application to 

 large trees is slow even with the most im- 

 proved machinery. (4) It has not yet 

 been demonstrated that spraying for the 

 control of walnut blight is very effective, 

 although there might be a cumulative 



* Walnut Culture in California, Walnut 

 Blight, California Experiment Station Bulletin 

 2S1. 



Circular 107, California Experiment Station. 



effect from a yearly application through 

 a long period of time. 



C. O. Smith, 

 University of California. 



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 pro- 

 duction in the large walnut-growing sec- 

 tions of the southern portion of the state. 



Trouble of this nature is quite com- 

 monly 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, gen- 

 erally speaking, to a loss of vitality in the 

 trees, brought about mostly by unavoid- 

 able mistakes made in planting when the 

 industry was new and experience in wal- 

 nut growing very limited. These mis- 

 takes are, briefly: 



1. Too close planting. The common 

 practice of setting 40 feet apart is not 



Walnut Blight in Foliage. 

 Fig. 4. Leaves Affected with Bacteriosis, Showing Diseased Vascular System, and Small 



Black Diseased Spots on Leaf. 



