86 The Spraying of Plants. 



During 1887 Koebele tested the value of the addition of 

 arsenic acid to kerose.ne emulsion. In his report to the Ento- 

 mologist, dated December, 1887, he says : l " In the main I have 

 followed your suggestion while here in April last, in preparing 

 the kerosene emulsion, viz. to emulsify with resin compound, 

 and use the arsenic acid in addition. I am glad that your 

 hopes in this wash are verified. In every instance where your 

 proposed arsenic acid was added, either to emulsified kerosene 

 or resin compound, there has been a complete extermination 

 of the scales." Although such washes were here favorably 

 reported upon, they have not come into general use. 



The next year another valuable contribution was made upon 

 this subject, of which the following abstracts are the most 

 important : 2 



"Caustic solutions have the disadvantage of hurting the 

 tree, and are not especially adapted to penetrate into the egg- 

 sac, which, on account of its peculiar texture, repels most 

 liquids. 



"Various soap solutions, some containing kerosene and some 

 whale-oil, have proved fair remedies, but cannot in my opinion 

 be equaled by the resin solutions, of which we give three 

 formulas. The first was tried by Mr. A. Koebele, the second 

 by Mr. Alexander Craw, of Los Angeles ; the third has been 

 given me by Mr. L. D. Green of Sacramento. From personal 

 experiments with them all I am well satisfied with them,, 



" Recipe No. 1. Four pounds resin, 3 pounds sal-soda, water 

 to make 36 pints. Dissolve the sal-soda in a few pints of water ; 

 when thoroughly dissolved, add the resin. Heat until dissolved, 

 and add water finally. Use two quarts of solution to the gallon 

 of water. Use at a temperature of about 100 F. 



" Recipe No. 2. One pound caustic soda, 10 pounds resin, 

 100 gallons water. Prepare as above. 



" As, perhaps, owing to the nature of the caustic, the leaves 

 are sometimes liable to be affected, I should recommend the 

 spraying of the tree with pure water liberally (the water will 

 free the pores of the leaves) two or three days after the appli- 

 cations of the resin solutions. 



1 Ann. liept. U. S. Com. of Agric. 1887, 143-147. 



2 Klee, " A Treatise on the Insect Injuries to Fruit and Fruit Trees of the 

 State of California," 1888, Oct. 12, 23, 20. 



