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 lj-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 l|-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 H-dosage schedule (dosage 

 schedule Xo. 1 increased one-half). Xo 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 H-dosage schedule, if 

 the work be carefullv 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 Xo. 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 



