INSECTICIDES AND FUNGICIDES. 11 



These indicate some of the possibiUties, but the principal action and the 

 contributory are generally difficult to define. These poisons are generally 

 soluble or emulsified products. They kill only by contact. Liberal and 

 thorough application is necessary to assure effectiveness, and drench 

 spraying is usually employed. The weaker the surface tension of the 

 spray and the thinner the chitin of the insect the more rapid the pene- 

 tration. 



The contact poisons that will be considered are (1) soaps, (2) sulfur 

 sprays, (3) oil sprays, (4) nicotine, and (5) pyrethrum. 



1. Soaps. 

 There are four different types of soap sprays, as follows: — 



1. Whale-oil or fish-oil soaps. 



2. Laundry soap. 



3. Rosin fish-oil soap, soap "stickers." 



4. Fish-oil soaps and nicotine. 



(1) Whale-oil or Fish-oil Soajis. 



Whale-oil soap was first brought forward in 1842 by the experiments 

 of Haggerston (19), and showed an efficiency which it has steadily main- 

 tained up to the present. It is interesting to note that many of the state- 

 ments made at that time in regard to its value have proved true through 

 years of subsequent use, and the dosage first recommended is practically 

 the same as that used to-day. 



At the present time soaps made from fish oil have largely supplanted 

 the true whale-oil soaps, but the similarity in the nature and effectiveness 

 of the two materials has led to the habit of using these two names more or 

 less interchangeably. Strictly speaking, however, the commercial product 

 to-day is largely made from various fish oils. 



For use as a summer spray against plant lice and other soft-bodied 

 insects,, as well as younger stages of more resistant types, it is very effective 

 when applied at the rate of 1 pound to 6-8 gallons of water, according to 

 the tenderness of the plant in question. It has sometimes been used for 

 dormant treatment of scale insects at the rate of 2 pounds to 1 gallon of 

 water, and applied while hot. The stronger, more efficient sulfur sprays 

 have largely supplanted it for this purpose. 



(2) Laundry Soap. 

 In the absence of whale-oil or fish-oil soaps, common laundry soap may 

 be employed effectively for the same type of insects. An average soap 

 of this type should be used at the rate of 1 pound to 2-4 gallons of water, 

 depending on the resistance of the insects treated. 



