64 DECIDUOUS FRUIT INSECTS AND INSECTICIDES. 
bodies and not penetrate to kill them. Both larvee and adults have 
been observed to actually float around in the ordinary soap and lime- 
sulphur sprays with no apparent inconvenience. Dry sprays are also 
absolutely ineffective. Emulsions of oil combined with crude car- 
bolic acid or crude creosote are extremely penetrating, in reality kill- 
ing almost every thrips that they touch, even when applied in a very 
weak form; but these combinations are just as violently injurious to 
blossoms and leaves as to thrips, consequently they can not be 
considered. Poisonous sprays are ineffective because the thrips feed 
from the inner parts of the plant and not from the outer layers, where 
the poison would be placed. 
Black-leaf tobacco extract diluted to proportions of 1 part extract 
to 50 of water has been very successful, but this spray seems to 
demand a somewhat heavier and more penetrating liquid than water 
alone as a carryingfagent. The distillate oil emulsion in 6 per cent 
dilution is almost as deadly as the black-leaf extract, but there will 
follow some injury from the spray unless conditions are altogether 
favorable. The oil spray has the advantage of being heavier, of 
being forced more easily into the buds, and of penetrating the oily 
coating offered by the thrips. This emulsion, however, reduced to a 
+ or 2 per cent solution, can be applied with safety to all trees, and 
when combined with black-leaf extract, diluted at the rate of 1 part 
of extract to 60 or 70 parts of water, furnishes a spray having all the 
required carrying, penetrating, and killing qualities desired. This 
is the spray which is now recommended. It can be applied with 
safety to opening buds, but should not be used on trees in full bloom. 
Blossom petals are more sensitive to injury from spraying than any 
other parts of a tree; but, since they soon fall, the damage, although 
noticeable, is not often serious. This spray can be applied to trees 
immediately after the blossoms have fallen, and later to the foliage 
for adults and larve. 
The first application should properly be made when the thrips are 
coming from the ground in large numbers and before the cluster buds 
are too far advanced. (See Pl. IV, showing stage of development of 
buds when first application should be made.) This period for the 
San Jose district of California is early in March, but it differs, of 
course, for the several varieties of fruits, as stated on page 54. 
Where the thrips are very numerous it may be necessary to imme- 
diately follow this first application with a second. Another applica- 
tion can be made immediately after the blossom petals fall, to kill 
the remaining adults, but more especially to kill the larve. The 
adults should by all means be attacked first. The spraying for larve 
is merely to alleviate the minor injury of scabbing on fruits, and to 
protect the trees for the following year by killing the larve before 
they get into the ground. 
