PESTS AND DISEASES OF PLANTS 219 



This spray is mixed as the preceding, and the iron sulphate after 

 being dissolved is added directly to the diluted mixture in the tank. 



The above spray is especially recommended for late summer sprayings 

 for red spider on almond and citrus trees, but should not be applied to 

 fruit trees just before the fruit is ready to pick, as the fruit might be 

 stained. 



For "self-boiled" lime sulphur see page 228. 



Lime-sulphur may be used in combination with tobacco sprays and 

 applied with safety on citrus trees prior to fumigation. It should not be 

 combined with Paris green, acid lead arsenate, zinc arsenite, oil emulsions 

 and soaps. With neutral lead arsenate, however, no damage may result. 



Emulsions and Miscible Oils. 



Emulsions are oil sprays in which soap is most frequently used as an 

 emulsifying agent. They have a high power of penetration and a rapid 

 and even distribution over the sprayed surface. With ordinary care they 

 may be readily made at home and are very valuable as insecticides. 



In the miscible oils the emulsifier is incorporated in the oil. The 

 proportions must be very exact and vary according to the variation in 

 the composition of the oil and other ingredients, and is therefore not 

 practical to be made at home. The miscible oil sprays are the highest 

 type of emulsions and are almost universally employed for commercial 

 purposes. 



Kerosene Emulsion. 



There are two general types of kerosene emulsion, as follows : 

 Cook Emulsion. In this emulsion there is a larger amount of soap. 

 It is the easiest to make, slightly more expensive and usually about as 

 effective if made with a good grade of fish oil soap. The general 

 formula is 



Fish oil soap 1 pound 



Kerosene J4 gallon 



Water 2 gallons 



This was the first attempt at making an emulsion of this type and 

 was a great discovery in insect control. It was invented by Dr. A. J. Cook 

 when at the Michigan Agricultural College. 



Riley-Hubbard Emulsion. In this emulsion the proportion of soap 

 does not vary far from l /^ pound to a gallon of oil. It requires very 

 vigorous agitation, the oil going quickly into the creamy condition of the 

 Cook emulsion, but after further agitation it thickens into a clabber-like 

 material. The formula is 



Fish oil soap y 2 pound 



Kerosene l /z gallon 



Water 1 gallon 



Preparation. The preparation of both of the above emulsions is about 

 the same and consists in first dissolving the soap in the hot water, after 

 which the kerosene is added and the whole thoroughly and vigorously 



