20, 2 Lee and Shino: Citrus-canker Control Experiments 189 
problem as to the theory of such action. It is hoped to advance 
further data that will narrow the scope of this problem. 
The previous conclusions advanced concerning the action of 
formalin solutions against Pseudomonas citri in vitro are en- 
tirely corroborated by the results of the present experiments. 
The field evidence would even support a stronger conclusion than 
that advanced, since trees sprayed with formalin 1 to 100 actually 
showed a greater percentage of canker than those untreated. 
This directly controverts the unfortunate recommendation of 
Kellerman,(2) in the Yearbook of the United States Department 
of Agriculture, in which he suggests formalin 1 to 100 solution 
as a spray in citrus-canker eradication work. Not, only would 
such a spray be a valueless expenditure of money, but field 
results indicate that the canker organisms may even have been 
disseminated by such a spray. 
The favorable bactericidal results obtained with lime sulphur 
in vitro are also borne out in the present field tests. How- 
ever, the lime-sulphur applications, since they are easily washed 
off by rains, do not show the same degree of preventive action 
as do the copper-precipitate sprays. Lime sulphur would be 
the preventive spray of unquestioned desirability, if means could 
be obtained for retaining it on the foliage. 
COSTS OF THE CONTROL MEASURES 
The foregoing conclusions being advanced, the question of 
the costs of these methods is immediately pertinent. The costs 
of the operations are shown in Tables 9, 10, and 11. 
TABLE 9.—Cost of labor in spraying operations; 238 trees. 
First application, June 3 and 6: Yen. 
Men: 564 hours = 9542 6-hour days, at Y 1.20 per 
day 11.30 
Work animals: 134 hours = 2%2 6-hour days, at 
Y 3 per day 6.75 
Total 18.05 
Cost per tree 0.075 
Second application, June 24 and 25: 
Men: 84 hours = 14 6-hour days, at Y 1.20 per 
day 16.80 
Work animals: 14 hours =24 6-hour days, at Y 
3 per day 7.00 
Total 23.80 
Cost per tree 0.10 
