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Slow action of insecticides on dormant scales. — An examination of the 
records of these experiments, in connection with results with other 
scale insects, strongly emphasizes the point that in the dormant resting 
condition scale insects respond to insecticides very slowly and grad- 
ually, and this has an important bearing on the determination of the 
usefulness of an application. The scale larvae during the growing sea- 
son are killed in a few minutes, or a few hours at farthest, just as 
other soft-bodied insects, but the mature scale does not for some time 
exhibit the effect of the wash unless it be so radically strong as to be 
unnecessarily expensive or as to endanger the life of the plant. It will 
be seen that little can be predicated of the ultimate result within two 
weeks, and at the end of a month the estimate can be only a provis- 
ional one. while at least two months are necessary to reach approxi- 
mately final conclusions. 
The slow progressive death of the scales must be largely due to the 
gradual penetration of the insecticide, and also indirectly to the soften- 
ing and loosening of the scale itself, enabling the weather conditions of 
moisture and cold to be more fatal. 
It will be noted, also, that it is the destruction of the last 5 or 6 per 
cent of the scale insects which necessitates the great strength of the 
wash and the accompanying heavy expense. It is comparatively easy 
to kill 15 to 90 per cent of the scales, and this with comparatively weak 
and inexpensive washes, but to reach the remaining few, double or 
treble strength is required.* 
Effect of the washes on the health of the tree and on the fruit. — With 
some of the stronger washes, particularly those of soap and resin, a 
marked diminution was shown in the amount of bloom and in the 
fruit set. This, however, was usually accompanied by au increase in 
the amount of foliage, and the results in this direction were especially 
marked in the cases of the two stronger whale-oil soap washes. The 
two trees so treated were noticeably vigorous in foliage, and presented 
a liner appearance than any in the orchard, but contained scarcely any 
fruit. The general effect of the washes on the trees was, however, in 
large measure vitiated by the damage already done them by the scale; 
and in most instances where there was a greater or less amount of 
injury, or the death of the tree resulted, it was due to the scale rather 
than the wash, as evidenced by the similar condition of adjoining 
untreated trees. The pure kerosene emulsion, however, had a disas- 
trous effect on the trees, and pure kerosene killed outright the trees 
treated with it. An application of soap made late in spring, or after 
the trees were already blooming, did not seem to affect seriously the 
setting of the fruit in the case of the peach, and in tin 1 case of the 
* This is illustrated notably in the resin wash experiments against Diaspis lauatus 
in the winter of 1894-93, where a double summer strength killed 90 per cent, an appli- 
cation twice as strong only 95 per cent, and one three times as strong, or six times- 
flummer strength, was necessary to effect complete extermination. 
