160 The Philippine Journal of Science 1921 
The observations presented in the tables were supplemented by 
a less complete and thorough observation, made in October, when 
it was found that, although some slight increase in canker had 
taken place in the case of the grapefruit varieties, the varieties 
of sweet orange and less susceptible species had maintained their 
comparative freedom from canker. The control obtained, there- 
fore, cannot be criticized as having been secured during seasons 
unfavorable to the activities of the citrus-canker organism, 
although advantage was taken of such an unfavorable period 
(the dry season, December to May), to minimize the dangers of 
reinfection during favorable periods (the wet season, June to 
November) . Such control as was obtained, in other words, was 
secured in the dry season and, except in the case of some of the 
grapefruit varieties, was maintained through the wet season, 
from June to October. 
Preventive sprays. — As to the comparative value of the dif- 
ferent spray mixtures as preventives, little can be concluded 
from the work at Lamao, because of the varied program for each 
plat. However, certain other factors developed which would 
eliminate or qualify the value of some of the mixtures. Thus 
copper sprays, if unaccompanied by scalecides, caused a great 
increase in scale insects ; lime sulphur probably could be used in 
regions of less intense rains, and in such cases would be of the 
greatest value because of its additional function as a scalecide; 
formalin 1 to 100 apparently was of little or no value as a 
preventive. 
The foregoing being the conclusions derived from the experi- 
ment, it also seems desirable to offer several suggestions for 
control procedures that became evident and that may be of value 
in future work. 
Clean-up sprays. — In many cases of heavily infected trees, a 
spray of formalin 1 to 80 caused a large proportion of the pre- 
viously weakened cankered leaves to drop; in other words, for- 
malin 1 to 80 to some extent seemed to be successful as a selective, 
clean-up spray. On trees already well infected such a clean-up 
spray, followed by careful pruning out of canker, materially 
hastened control. 
Stimulation of growth at climatic periods unfavorable for 
canker development. — Another more important point was the 
stimulation of new growth at periods in the year when the lack 
of moisture limited the activity of the canker organism. At 
Lamao such new growth was stimulated in the early part of 
