46 FUMIGATION INVESTIGATIONS IN CALIFOENIA. 



ERADICATION OF THE PURPLE SCALE. 



The foregoing experiments have shown that the purple scale can 

 be eradicated from citrus trees, provided a dosage of sufficient 

 strength be used with a sufficient exposure. This dosage strength 

 is much greater than that at present used in fumigation. 



If the purple scale can be everywhere eradicated by using a dosage 

 of definite strength (which we hope to determine in due time), the 

 question will immediately arise in the orchardist's mind whether it 

 will be profitable to use this heavier dosage provided it can be em- 

 ployed without injury to the tree and fruit. In deciding this ques- 

 tion several practical considerations must be taken into account. 

 The trees, as will be shown later, are in a condition to stand this 

 heavy dosage without injury during but a limited portion of the year. 

 It would be impossible for the number of outfits at present in exist- 

 ence to fumigate the infested area within this limit of time. More- 

 over, unless compelled to do so the orchardists in any locality would 

 not all use this dosage. Whether it would be advisable for a grower 

 to incur the additional expense for this heavier dosage in his orchard 

 when the infested orchards on all sides of him are fumigated with 

 lighter dosages, if at all, must be determined by large-scale tests. 

 The foregoing are some of the difficulties in respect to the use of this 

 heavy dosage. 



DIFFICULTY OF DESTROYING THE SCALE ON THE FRUIT. 



There is one more important point which must be considered in 

 connection with fumigation for the purple scale. It will be seen in 

 an examination of the data from the foregoing experiments that an 

 orchardist, fumigating trees containing purple scale in its different 

 stages on the fruit as well as on the leaves and branches, would, 

 except with the heaviest dosages, leave on the fruit healthy eggs soon 

 to hatch and infest other parts of the trees. It would be impractical 

 under most circumstances to use a dosage heavy enough to destroy 

 the eggs on the fruit. The cost of the extra cyanid required, above 

 that necessary for the destruction of the eggs on the leaves and 

 branches, would be more than the scaly fruit is worth. Therefore 

 in fumigating for eradication it is advisable to remove the infested 

 fruit, and it is advisable to remove the old scaly fruit in any fumi- 

 gation. At picking, fruit badly infested with scale is usually left 

 on the tree, and frequently from one to a half dozen or more old, 

 scale-infested oranges per tree remain throughout an orchard. Even 

 after a good fumigation one of these old fruits might carry more 

 healthy purple-scale eggs than all the rest of the tree, and on the 

 hatching of these eggs the insects will spread to other parts of the 

 tree. The danger from old scaly fruit is evident and all such should 

 be removed from the trees before fumigating an orchard. 



