FUMIGATION OF CITRUS TREES. 55 
LENGTH OF EXPOSURE. 
Experiments against the purple scale showed that in using a 2-ounce 
dosage rate eradication occurred on the leaves and branches with a 
30-minutes exposure, whereas with a one-hour exposure it was pos- 
sible to accomplish the same results by using a 1 J-ounce dosage rate. 
This demonstrates that decidedly better results can be secured by 
leaving the tents on the trees one hour than is possible with 30 
minutes of gassing. With the present character of tents in use 
practically all gas has escaped on most nights by the end of an hour. 
This furnishes sufficient evidence that a longer exposure would be 
unnecessary. However, experiments have been carried on in which 
exposures of greater duration than one hour were made, but no 
better killing resulted. From all the experimental evidence at hand, 
an exposure of one hour is advised for the purple scale. This length 
of time readily enables an outfit to go through the complete operation 
of preparing the chemicals and dosing the trees, with a few minutes 
to spare for rest. 
ERADICATION. 
Experiments during the earlier part of the investigation showed that 
the purple scale could be eradicated from the leaves and branches of 
trees by using a dosage equivalent to a 1 ^-dosage schedule. During 
the first part of September, 1908, an isolated orange orchard containing 
about 1 acre of trees from 10 to 18 feet tall and severely infested with 
the purple scale was fumigated, using a 1 ^-dosage schedule (dosage 
schedule No. 1 increased one-half). No old scaly fruit was left on the 
trees. The results were as follows: An inspection of this orchard 
during the latter part of the autumn failed to reveal any live insects. 
The crop of fruit on the trees was entirely free of scale for the first time 
in the memory of the owner. Many examinations have been made 
since, yet without the finding of a single live insect. 
This experiment has shown that eradication of the purple scale on 
trees free of infested fruit is possible with a 1 ^-dosage schedule, if 
the work be carefully done. In small isolated orchards it might be 
practicable at certain times to use this dosage. For general work 
the employment of this eradication dosage is not advised. The 
writer's experience has assured him that careful work under the most 
favorable conditions would largely avoid pitting of fruit even with 
this high dosage. But, as a matter of fact, the work in the field is not 
always carefully done, nor are the most favorable conditions always 
taken advantage of. Experience has shown that the pitting of fruit 
with regular schedule No. 1 sometimes causes a slight dissatisfaction 
among growers. If the injury from schedule No. 1 sometimes pro- 
duces dissatisfaction, it is very evident that the greater risk with a 
larger dosage is too great to justify its general adoption. 
67330°— Bull. 90—12 5 
