INSECTICIDES AND FUNGICIDES. 19 



emulsion, but remains in a more or less fluid condition. It should be 

 diluted 1 part to 25-30 of water, and applied to the ground around the 

 stems. Its use is restricted to small areas. 



(2) Mlscible Oils. 



]Miscible oils are formed from a mineral oil emulsified with a vegetable 

 oil, with some alkali present. A stable stock emulsion is formed which 

 mixes readily with water. These preparations are particularly adapted 

 for use on old, rough-barked trees heavily encrusted with scale, as the oils 

 spread over the bark more readily than do sulfur sprays. As the propor- 

 tion of component parts is seldom furnished, and the manufacture of these 

 oils is, in fact, more or less of a trade secret, the directions furnished by the 

 manufacturer, both as to dilution and application, should be very carefully 

 followed, whatever brand is used. In general, for dormant spraj'ing these 

 oils are diluted at the rate of 1 part to 12-15 parts of water. 



The use of these oils has sometimes been followed by distinct injury, 

 even where proper precautions ha^'e been taken and directions carefully 

 followed. There are also reports of cumulative injurj^ following repeated 

 applications (29). 



Miscible oils are relatively expensive dormant spraj^s in spite of the fact 

 that the oil is said to go further in application than an equal aiiiount of 

 lime-sulfur. The uncertainty of the exact effect of the oils upon the health 

 of the tree seems to favor the use of lime-sulfur, which has proved to be 

 an efficient scale destroyer and can be used with safety. 



4. Nicotine. 



The value of tobacco in killing soft-bodied types of insects was dis- 

 covered very early. In 1763 it w^as recommended in France for the control 

 of plant lice, both tobacco powder and a water solution being applied. 

 Its use in America was first recorded in 1814. Its effectiveness against 

 soft-bodied insects and its safety to foliage of plants soon gave it a prom- 

 inence which has continued undiminished to the present clay. The most 

 active principle of tobacco, and the one which gives it its value as an 

 insecticide, is the alkaloid, nicotine. Soluble in water, entirely volatile, 

 this is one of the most virulent poisons known. 



(1) Nicotine Sulfate. 

 At the present time there are on the market a number of different 

 commercial brands of nicotine, of various grades and strengths, which 

 have to a large extent superseded the home-made preparations for general 

 use. For garden and orchard operations the highly concentrated product 

 containing 40 per cent of nicotine in the form of nicotine sulfate is at 

 present extensively used. This is sold under various trade names, as 

 "Black-Leaf 40," "Nicotine Sulfate 40%," etc. It has proved especially 

 valuable for the control of many soft-bodied sucking insects.^ It can be 



