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Lee: Citrus-canker Control 
165 
December 29, 1917. Yothers’s oil emulsion plus formalin 1-100. 
February 6, 1918. Cresol-kerosene emulsion. 
May 20, 1918. Neutral Bordeaux mixture. 
June 10, 1918. Neutral Bordeaux mixture. 
July 6, 1918. Neutral Bordeaux mixture plus cresol-kerosene emul- 
sion. 
The plan of this spray campaign was to use several applica- 
tions of strong formalin solution as clean-up sprays at first, in 
order to reduce the amounts of citrus canker infection and so 
lessen the work of pruning out the cankered twigs and foliage. 
The trees were in many cases partially defoliated by these strong 
formalin sprays, but for the most part the cankered leaves were 
the ones to fall. The formalin sprays were followed by an ex- 
tremely careful pruning out of all twig cankers. Having at- 
tempted entirely to remove all the sources of infection in this 
way, prevention of new infection was attempted by the applica- 
tion of Bordeaux mixture. No spraying of the soil was carried 
on in as much as it had been shown by the present writer (10) 
that the canker bacteria are quickly killed out in Philippine 
orchard soils. The character of the trees and the results of 
these treatments are shown in Table 14. 
From the viewpoint of total eradication it is to be seen that this 
experiment yielded negative results. After the initial careful 
removal of all sources of infection there were recurrences of 
canker in a number of cases. In the small planting employed 
in this experiment such recurrences were noted promptly and 
removed ; in a large commercial planting of susceptible trees such 
close observation could not be maintained with financial profit. 
In this connection, however, consideration should also be given 
to the susceptibility of the host under treatment. Thus, although 
it is evident that such attempts at eradication were unsuccessful 
on the very susceptible lime varieties, a very exhaustive experi- 
ment would be necessary upon a planting exclusively of trees 
of the mandarin orange or Satsuma orange varieties before a 
similar conclusion could be adopted for such a host. 
To avoid confusion it should be made clear that, although 
calamondin and mandarin orange trees when mature are consid- 
ered resistant to citrus canker, they will exhibit a considerably 
greater degree of susceptibility when young in nursery rows. 
This has been pointed out more in detail previously by the pres- 
ent writer. (12) 
