THE CITRUS THRIPS. 37 



centage of the thrips can be killed by spraying with this solution, and 

 there is a further effectiveness due to its decomposition for a long 

 period after deposition on the leaves. In orchards sprayed with 

 good lime-sulphur the sulphurous odor is often strong for two months 

 or more after the applications. The decomposition products repel 

 the thrips, which are slower to reinfest orchards so sprayed than 

 those sprayed with solutions that soon evaporate and leave no trace. 



Tobacco extracts when used at the proper strengths are also very 

 effective. Both tobacco extract and lime-sulphur, when mixed to- 

 gether, are effective in weaker solutions than when diluted with water 

 alone. Contrary to expectation, the addition of soaps to tobacco 

 extract did not give increased value to the tobacco in these tests. 

 Soap solutions used alone appear to be worthless at the dilutions 

 tested. 



Resin wash at any strength practicable for use on the orange trees 

 in this section is worthless. At the greatest strength used in these 

 experiments it failed to reduce thrips injury to an extent worthy of 

 attention. It is, furthermore, very injurious to fruit and foliage. 



Plain tvater spraying was utterly ineffective, demonstrating that 

 merely striking the thrips with a liquid at high pressure to wash 

 them from the trees has no appreciable effect in diminishing their 

 numbers. A few hours after spraying with water there remained 

 on the trees as many living, active thrips as before spraying. 



INJURIES TO CITRUS RESULTING FROM SPRAYING. 



INJUKY FROM DISTILLATE-OIL EMULSION. 



In experiments conducted in 1910, emulsions containing 2 per cent 

 of distillate oil caused severe staining to ripe oranges. Dark streaks 

 were formed on the rind where the liquid had collected in drops and 

 run down. A patent spray emulsion caused more staining than the 

 home product at the same strength. 



INJURY FROM RESIN WASH. 



On July 20, 1911, about two weeks after the final spray applica- 

 tion, injury appeared from the resin wash in plat 18, Series I. About 

 3 per cent of the leaves had turned brown and fallen and most of 

 the oranges had become spotted with the varnish. In some cases the 

 varnish had collected in drops and run down over the surface, finally 

 drying to a hard, gummy substance. By September 25 the injury 

 apparently had reached its highest degree and was serious in all 

 three plats, though noticeably decreasing with the greater dilution 

 of the wash. The epidermal cells of fruit protected from the direct 

 rays of the sun were killed and a shallow, brown scab was formed. 

 This scab often peeled off, leaving a film of light gray-green tissue 



