168 
The Philippine Journal of Science 
1921 
DISCUSSION OF RESULTS AND THEIR APPLICATION 
In the Philippines it would seem to be possible, by the selec- 
tion of the proper varieties and the use of the methods described 
previously, to raise citrus fruits free from citrus canker. How- 
ever, in other countries, as in Florida, where the susceptible 
grapefruit and lime varieties are already planted and very 
largely grown, control of such very susceptible varieties by the 
methods employed here would be very expensive and apparently 
not economically feasible. It seems safe to conclude that the 
practical control or the prevention of citrus canker by the pres- 
ent known methods on very susceptible hosts, such as the 
American-grown grapefruit varieties and the West Indian limes, 
can only be accomplished by the total exclusion of the disease 
from entire localities; this conclusion possibly would not apply 
to arid or semiarid countries. An alternative would be the 
securing of resistant varieties of these species, either by breed- 
ing or from among the little-known, already existing varieties 
of the East Indies and Southern Asia. 7 
In regions of the United States where the very susceptible 
lime and grapefruit varieties are not grown, control upon the 
less susceptible varieties by these methods would be possible, but 
the economic feasibility of these methods is not yet proven. In 
some regions, as in Alabama and Mississippi, where only slightly 
susceptible varieties such as the Satsuma strains are grown com- 
mercially, control methods would be practicable or even unnec- 
essary. . 
SUMMARY 
1. The development of the experiments has shown that in 
addition to preventive sprays the following factors contributed 
very largely to minimizing canker infection : Removal of sources 
of infection by pruning and drastic “clean-up” sprays; stimula- 
tion of foliage growth to occur at periods of the year unfavorable 
to canker dissemination or development; the control of violent 
winds by windbreaks and orchard situation ; and the control of 
chewing insects. 
7 The writer has obtained pummelos in Hongkong, imported from Saigon 
and Bangkok, which were entirely free from citrus canker; they were 
commercially seedless and possessed the desirable flavor and texture of 
the American-grown grapefruit. 
