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Lee: Citrus-canker Control 
169 
2. The preventive sprays used with any degree of success 
were Bordeaux mixtures and Burgundy mixtures of various 
concentrations. Lime sulphur, formalin, and ammoniacal cop- 
per carbonate solutions were unsuccessful under Philippine 
rainy season conditions. Copper sprays were not wholly suc- 
cessful, although they effected tangible reductions in canker 
infections. 
3. The work has made apparent, and it has been one of the 
principal objects in the presentation of this paper to point this 
out, that the most important consideration in discussing the feasi- 
bility of control, the seriousness of citrus canker, and such 
subjects, is a knowledge of the reaction to the disease of the 
different species and horticultural varieties. The wide range 
in the susceptibility of the Citrus species necessitates the 
separate discussion of canker-control possibilities for each host 
or class of hosts. 
4. The conclusion is apparently safe that control upon the 
very susceptible lime and grapefruit varieties is not economical- 
ly feasible by the methods employed. Upon the sweet oranges 
of Florida origin and such varieties of less susceptiblility, con- 
trol may be practicable; further work is now in progress upon 
this point. The sweet orange of the so-called Mediterranean 
varieties, some of the lemons, and the Unshiu orange varie- 
ties comprise a class of fruits of very moderate susceptibility; 
control apparently would be economically practicable on such 
varieties. Control was very easily obtained and was hardly 
necessary upon the mandarin orange varieties, the calamondins, 
and the citrons. Attention has been called to several exceptions 
from the extreme susceptibility of the lime and grapefruit 
varieties; such exceptions may be of value for cultivation in 
regions of universal distribution of citrus canker. 
5. An attempt to obtain complete eradication of citrus can- 
ker without the total destruction of the trees was conducted on 
a small isolated plat of calamondin, mandarin orange, and lime 
trees. From the viewpoint of total eradication, negative results 
were obtained on this plat. In this case, as in others, the results 
must be considered in connection with the Citrus species used 
as hosts in the experiment. Thus these results, although ap- 
plicable to the limes, and probably to the grapefruits, should 
not be considered applicable to the less susceptible varieties, 
such as the mandarin and Satsuma oranges, until more ex- 
