68 Subtropical Vegetable-Gardening 



dusted over the plants in place of being applied as a 

 liquid. 



Zinc arsenite is a new arsenical compound that has shown 

 itself to be applicable where lead arsenate may prove too 

 caustic. It usually comes in a powdered form. One 

 pound of zinc arsenite to 50 gallons of water should be 

 used, or it may be mixed with flour or air-slaked lime and 

 dusted on, as in the case of paris green and powdered 

 lead arsenate. 



CONTACT INSECTICIDES 



The success attained by using the poisonous insecticides 

 gave a strong impetus to the investigation which had for 

 its purpose the control of insects that feed from the in- 

 terior of the plants and so are immune from poisonous 

 insecticides. 



Kerosene emulsion was the first of the contact insecti- 

 cides that came into general use. It is rather easy to 

 prepare, and since kerosene (coal oil) is found almost con- 

 stantly in the farm home, it can be made up without 

 much difficulty. One-half pound of hard soap should be 

 dissolved in 1 gallon of water. This can be done best by 

 chipping the soap and letting it drop into boiling water. 

 The soap solution should be removed from the fire, and 

 2 gallons of kerosene poured into it. Then the mixture 

 should be thoroughly agitated by means of the spraying 

 pump. In a short time a thick, creamy mass will have 

 formed. The hotter the water, the quicker the emulsion 

 will form. As soon as no free oil forms at the top of the 

 emulsion on straining, the emulsion may be said to be 



