9 



These two materials may be applied in such quantities as to furnish 

 approximately equivalent amounts of soluble sulfur. On the basis of 

 amounts of soluble sulfur equal to the standard application of 33° Baum6 

 lime-sulfur concentrate, the following table is presented as showing sug- 

 gested formulas for application : — 



Formulas for Application. 



' This amount is greater than is recommended by the manufacturers. 



For the different strengths of lime-sulfur concentrate which may be 

 prepared or which are already on the market, Table I, on page 14, gives 

 information as to formula for application. 



(S) Oil Sprays. 



Oil sprays probably owe their insecticidal value chiefly to their asphyxi- 

 ating effect. To a certain degree some of them may also have corrosive 

 effect. Oil sprays have a peculiar creeping power which enables the 

 operator to cover the tree even under unfavorable spraying conditions, 

 while with most other contact insecticides an insect to be killed must be 

 actually hit. The oil sprays, however, are not sold under any standard 

 form of guaranty. 



(4) Nicotine. 



A number of different commercial brands of nicotine of various grades 

 and strength are now on the market. For garden and orchard operations 

 the highly concentrated product guaranteeing 40 per cent of nicotine in 

 the form of nicotine sulfate is at present most extensively used. This 

 has proved especially valuable for the control of many soft-bodied insects. 



B. FUNGICIDES. 



Fungicides are substances used to kill or prevent the growth of fungi. 

 They are applied to the host as spraj^, dust or fumes. For the most part, 

 they are used as preventives and not cures, and therefore should be applied 

 before the fungus is present on the surface of the host plant. As such, 

 they protect by forming a poison barrier through which the threatening 

 fungus cannot penetrate. Sometimes, however, they are used to destroy 

 a pathogen (parasitic organism which causes the disease) which is already 

 present, — e.g., powdery mildews and potato tuber organisms, — in which 



