64 THE SAN JOSE SCALE. 
while elsewhere a considerable percentage of living scales will be found, 
sometimes confined to small areas. This is due either to a failure to 
drench the tree evenly or else to the action of subsequent rains and 
snows. The latter causes affected. in this way some midwinter experi- 
ments conducted by us, which in one instance were followed by a light 
rain of a few minutes' duration from the northwest, and in another were 
affected by the irregular melting of snow, which lodged to a considerable 
extent in the trees. 
These facts afford an additional reason for making the treatment 
early in the fall, so that the wash may act over as long a period as possi- 
ble, since at this season rains are usually much less frequent than they 
are in mid or late winter or early spring. 
Action of insecticides on dormant scales. — An examination of the rec- 
ords of these experiments, in connection with results with other scale 
insects, strongly emphasizes the point that in the dormant resting con- 
dition scale insects respond to insecticides very slowly and gradually, 
and this has an important bearing on the determination of the useful- 
ness of an application. The scale larvae during the growing season 
are killed in a few minutes, or a few hours at furthest, just as are other 
soft-bodied insects, but the mature scale does not exhibit the effect of 
the wash for some time unless it be so radically strong as to be unnec- 
essarily expensive or as to endanger the life of the plant. We found 
that little could be judged of the ultimate result within two weeks, 
and at the end of a month the estimate could be only a provisional one, 
while at least two months were necessary to reach approximately final 
conclusions. 
The slow and progressive death of the scales must be largely due to 
the gradual penetration of the insecticide, and also indirectly to the 
softening and loosening of the scale itself, enabling subsequent weather 
conditions of moisture and cold to be more fatal. 
It was 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 75 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. 1 
Effect of the ivaslies on the health of the tree and on fruiting. — With 
some of the stronger washes, particularly those of soap and resin, 
a marked diminution is shown in the amount of bloom and in the 
fruit set. This, however, is usually accompanied by an increase in the 
amount of foliage. This was very marked in the case of the trees 
treated with the stronger whale-oil soap washes, which were noticeably 
1 This is illustrated notably in the resin wash experiments against Diaspis lanatus 
in the winter of 1894-95, where a double summer strength killed 90 per cent; an 
application twice as strong, only 95 per cent; and one three times as strong, or six 
times summer strength, was necessary to effect complete extermination. 
