12 



BULLETIN 938, U. S. DEPARTMENT OF AGRICULTURE. 



To determine how long nicotine sulphate may remain on fruit-tree 

 foliage after the application of the spray solution, the following ex- 

 periments were performed by Mclndoo. On September 10 a small 

 pear tree was sprayed with a solution of commercial 40 per cent 

 nicotine sulphate 1 : 800, containing fish-oil soap (2 pounds to 100 

 gallons water). On various days thereafter about a quart of the 

 spra} T ed leaves were collected on each recorded date : the leaves, after 

 being ground in a meat grinder, were then mixed thoroughly with 

 water containing sodium carbonate. Upon distilling this mixture a 

 distillate containing nicotine was obtained on each day tested up to 

 the thirty-fifth day after the leaves had been sprayed. On the forty- 

 second day after applying the spray solution only an indication of a 

 precipitate was observed, but concluding from the precipitates ob- 

 tained prior to this date the amounts of nicotine present in the 

 distillates seemed to decrease irregularly from the first to the forty- 

 second day ; soon after which the remaining leaves fell from the trees. 

 During these tests there was comparatively little rainfall ; neverthe- 

 less the results of the tests indicate that considerable rainfall is 

 required to remove all of the nicotine sulphate adhering to the sprayed 

 leaves. The details of these tests are presented in Table IV : 



Table IV. — Tests on various dates using pear-tree leaves which had been 

 sprayed on Sept. 10 with a solution of commercial Ifi per cent nicotine sul- 

 phate (1:800) containing soap to slioic the presence of nicotine. 





Number 



of days 



after 



leaves 



had been 



sprayed. 



Kind of precipitate 

 obtained using — 



Amount 

 of 



rainfall. 





Pate. 



Phospho- 



molybdic 



acid. 



Silico- 



tungstic 



acid. 



Remarks. 



Sept. 11 



Sept. 12 

 Sept. 12 

 Sept. 13 

 Sept. 14 

 Sept. 15 

 Sept. 16 

 Sept. 18 

 Sept. 24 

 Sept. 27 

 Sept. 28 

 Oct. 1 

 Oct. 4 



1 

 2 



C 1 ) 



3 



4 



5 



6 



8 



14 



17 



18 



21 



24 



25 



28 



29 



31 



32 



35 



39 



40 



42 



Heavy 



...do 



None 



Heavy 



...do 



Heavy 



...do 



None 



Heavv 



...do.: 



Incites. 

 0.00 

 .00 

 .00 

 .00 

 .14 

 .01 

 .08 

 .00 



T. 

 .07 

 .16 

 .00 

 .01 

 .20 

 .07 

 .35 

 .01 

 .36 



T. 

 .89 

 .01 



Spraved leaves emit nicotinelike odor. 



Do. 

 Pnsprayed leaves on another tree were used. 

 Sprayed leaves do not emit nicotinelike odor. 









Fair 



...do 



Faint 



Very faint. 











Fair 



Very faint. 





Oct. 5 









Oct. 8 

 Oct. 9 



Fair 



None 





Oct. 11 









Oct. 12 









Oct. 15 

 Oct. 19 



Very faint . 



None 





Oct. 20 









Oct. 22 



Indication. 



None 













Total amount of rainfall during tests. . . 



2.36 





1 Control. 



