6 ■ BULLETIN 611, U. S. DEPARTMENT OF AGRICULTURE. 



so successful as in the control of those due to fungi; until the efficacy 

 of spraying may have become established, too much should not be 

 expected from this method of control. 



A logical and seemingly practicable method of avoiding losses inci- 

 dent to bacteriosis is in the possible development of immune or highly 

 resistant varieties. Work along this line is now under way on the 

 Pacific coast, but it is not known that any varieties altogether re- 

 sistant to blight or even practically immune to it have thus far been 

 brought to light. However, among the many thousands of seedling 

 trees on the Pacific coast and the. hundreds in the eastern United 

 States, it would not seem too much to presume that for general 

 orchard planting blight-resistant and otherwise desirable varieties 

 will yet be found. Whenever such varieties are discovered, arrange- 

 ments may be made with the Department of Agriculture for testing 

 their susceptibility to this disease by means of inoculation experi- 

 ments. Meanwhile, it is to be hoped that the planting of small com- 

 mercial orchards and of trees for home use will be continued, as small 

 groups of bearing trees over a wide range of territory will furnish 

 valuable suggestions as to future commercial plantings. 



SUMMARY. 



Walnut blight, or bacteriosis, is distributed very generally through- 

 out the eastern half of the country. Investigations by Mr. M. B. 

 Waite and the writer have demonstrated its occurrence in Louisiana, 

 the District of Columbia, Maryland, Delaware, Pennsylvania, and 

 New York, and there seems to be no reason to suppose that it will 

 not occur wherever Persian walnuts are grown in the United States. 



During the summer of 1916 pure cultures of the causal organism 

 were obtained from naturally infected nuts; inoculation experiments 

 were conducted in healthy nuts and twigs, and these inoculations were 

 uniformly successful in producing the disease. Cultural studies were 

 conducted in the laboratory, and the results obtained corresponded 

 with those reported by Pierce * and by Smith. 2 



The writer's observations of this disease have covered one season 

 only, and therefore definite conclusions as to its behavior under vary- 

 ing seasonal conditions are not possible. It may be stated, however, 

 that late infections were the rule during the season of 1916, and if 

 this condition holds generally true from season to season it will con- 

 stitute a striking difference between the behavior of the disease in the 

 Middle Atlantic States and on the Pacific coast. 



Extensive experiments to control this disease by spraying have 

 been conducted from time to time in California, but the results ob- 

 tained have never been entirely satisfactory. Here, again, the differ- 



* Pierce, N. B. Op, eit, * SBaito 8 B, EL f Smith, C. 0., and Ramsey f H. J. Op. eifc 



