2 Department Circular 376, U. S. Dept. of Agriculture 
obscure disease by Erwin F. Smith and his associates in 1907 marked 
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 concerning 
the identification of this 
disease. 
EXPERIMENTS AND 
RESULTS 
As early as 1909 the sen- 
lor writer used a formal- 
dehyde solution as a dip 
for apple stocks and scions 
before grafting, as a means 
of controlling crown gall. 
Observations always indi- 
cated the practicability of 
this method, and accord- 
ingly nurserymen have been 
advised in correspondence 
as to this treatment for at 
least a decade. The need 
of more exact knowledge 
. ck was so apparent that in 
Fic. 1—Typical trees classified as clean 1921 experiments were ini- 
tiated in an attempt to ob- 
tain 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 modifications 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 distinctly more efficacious 
than the formaldehyde-solution treatment. Mercury compounds are 
among the most powerful of germicides; but the morganic com- 
pounds, 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 
