FUMIGATION OF CITRUS TREES. 
59 
THE BLACK SCALE. 
To specify a certain dosage for use at all times against the black 
scale is impractical. The reason is that this insect is more difficult 
to destroy in some stages of its development than in others. While 
young and in a soft condition it can be destroyed by a light dosage. 
As the insect approaches maturity its body becomes leathery and 
tough, which renders it difficult to destroy. The eggs require even 
a heavier dosage. The great variation in development among the 
black scale results that at most times of the year trees will contain 
insects in all stages of development, from those recently hatched to 
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2S 
43 
Fig. 11.— Dosage schedule No. f, for potassium cyauid. (Original.) 
tough or even leathery ones. In such cases a dosage sufficient to 
destroy the more resistant individuals is necessary. 
Experiments during this investigation, as well as observation of the 
work of practical outfits, has demonstrated that in the younger and 
tenderer stages this insect can be destroyed by one-half of schedule 
No. 1. Very few of those in the later stages of development are 
affected by such a dosage. A three-fourths schedule not only 
destroyed those in the earlier stages of development, but also those 
of a leathery nature and many that are tough and full grown, as 
evidenced by their size, together with the absence of the character- 
istic letter "H" on the upper side. A considerable percentage of 
eggs is also destroyed at this strength. A full schedule No. 1 dosage 
