2 CIRCULAR 3 7 6, U. S. DEPARTMENT OF AGRICULTURE 



a real epoch in the history of crown gall and appeared to open possi- 

 bilities of finding satisfactory and practical remedies for the trouble. 

 Nevertheless, in so far as the control of crown gall in the apple 

 nursery is concerned, no very extensive practical applications of 

 these important discoveries have as yet materialized. 



This circular is published for the purpose of making immediately 

 available to nurserymen and others interested in the propagation 

 and growing of root-grafted apple trees in nurseries a new method 

 of greatly reducing the attacks of crown gall. This preliminary 

 report, to be followed later by a technical paper containing full 

 details, also discusses briefly certain problems concerning the diag- 

 nosis of crown gall. It is hoped that the results of these experiments 



will tend to answer some 

 of the questions concern- 

 ing the identification of 

 this disease. 



EXPERIMENTS AND 

 RESULTS 



As early as 1909 the 

 senior writer used a for- 

 maldehyde solution as a 

 dip for apple stocks and 

 scions before grafting, as 

 a means of controlling 

 crown gall. Observations^ 

 always indicated the prac- 

 ticability of this method, 

 and nurserymen accord- 

 ingly have been advised in 

 correspondence as to this 

 treatment for at least a 

 decade. The need of 

 more exact knowledge 



Fig. 1.— Typical trees classified as clean waS SO apparent that in 



1921 experiments were 

 initiated in an attempt to obtain more definite information on this 

 phase as well as on related phases of the subject. This investigation, 

 covering a period of five years, appears to confirm conclusively the 

 observations of the writers extending over a much longer period. In 

 these experiments this formaldehyde-solution treatment with modifi- 

 cations has consistently proved of value in controlling the crown-gall 

 disease on apple grafts. For the past three years one of the organic- 

 mercury compounds has also been tested as a dip and has proved dis- 

 tinctly more efficacious than the formaldehyde-solution treatment. 

 Mercury compounds are among the most powerful of germicides, but 

 the inorganic compounds, such as corrosive sublimate, are often very 

 injurious to plant life, even in extremely dilute solutions. A number 

 of new organic-mercury compounds have recently been put on the 

 market and have proved of value in the control of other plant diseases. 

 This particular one was tried in the hope that it would be effective 

 in controlling crown gall and would be noninjurious to the apple 



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