280 CONTROLLING INSECTS AND DISEASES 



lubricating oils are very dangerous if the buds have swollen, 

 if the material is not properly emulsified, or if the mixture 

 is not fresh. Otherwise they give good results. 



White oils are highly refined mineral oils which have 

 been used on summer foliage and possibly have a place in the 

 spraying program of the future. Their greatest disadvantage 

 is that they burn foliage which carries a sulfur residue. 



This whole subject of the effectiveness of oil sprays of 

 various types and the proper time of application is now in 

 a state of flux. Interest is keen, and developments should 

 be watched carefully. A report on the subject (Table 39) 

 issued by the New York Agricultural Experiment Station at 

 Geneva indicates the present status of oil sprays in early 

 spring applications. The desire is to use some economical, 

 safe material that will control as many pests as possible in 

 the smallest number of applications. 



a : 9. Soaps in combination with water possess insecticidal 

 properties. They are seldom used alone but rather as constitu- 

 ents of oil emulsions or miscible oils, or in nicotine sprays to 

 increase their spreading properties and liberate the nicotine. 

 Potash fish-oil soap is the common form. Soda fish-oil soap 

 will not dissolve so easily. Resin fish oil will not curdle in 

 hard water. 



a : 10. Less Common Contact Insecticides. Pyrethrum is 

 a powder made from the flower heads of three species of pyr- 

 ethrum plants. It is non-poisondus to warm blooded animals, 

 but it loses its toxic properties upon exposure and it is difficult 

 to find methods of standardization. Rotenone is both a con- 

 tact and stomach poison which is harmless to warm-blooded 

 animals. It is found in the roots of the derris plant in the 

 Malay Peninsula and in cube which grows in Peru. Although 

 it is known to be a very good insecticide, its use is limited 

 because of the cost of importing the raw material. Elgetol 

 is a bright yellow dyestuff which is of value as an insecticide 

 and ovicide and for which claims are made as a fungicide. 

 It has been used thus far chiefly in the dormant or "bud-break- 



