64 DECIDUOUS FRUIT INSECTS AND INSECTICIDES. 



bodies and not penetrate to kill them. Both larvae 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 carrying agent. 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 

 H 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 larvse. 



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 larvse. The 

 adults should by all means be attacked first. The spraying for larvse 

 is merely to alleviate the minor injmy of scabbing on fruits, and to 

 protect the trees for the following year by killing the larvse before 

 they get into the ground. 



