160 PRINCIPLES OF PLANT CULTURE 



applied as sprays. Nicotine sulfate is a more recent 

 spray material with similar properties which has largely 

 replaced the other forms of tobacco sprays with com- 

 mercial growers. 



294. Kerosene is a very useful insecticide for a class 

 of insects not readily destroyed by other means (316). 

 It has generally been used as an emulsion made with 

 soap and water, for which the following formula is 

 good : 



Dissolve one-half pound of hard soap in one gallon 

 of boiling soft water ; add at once two gallons of kerosene, 

 and churn or otherwise violently agitate for five or ten 

 minutes. 



This is a stock solution and must be diluted before use. 

 The amount of dilution depends upon the season of the 

 year when applied, the kind of plant to which applied 

 and the insect to be controlled. When plants are dormant 

 it may be put on as strong as 25 per cent kerosene. It 

 may be applied, when the plants are in leaf, much stronger 

 on apples and other hardy-leaved plants than it can to 

 tender-foliage plants, as peach. It will need to be stronger 

 to control some insects than others. For plant-lice, 

 against which it is commonly used, the usual strength is 

 about five to seven per cent. 



295. Lime sulfur wash is largely used for the control 

 of scale insects. The wash is prepared by boiling to- 

 gether definite amounts of stone lime and powdered 

 sulfur. As this material can be secured upon the 

 market in commercial form, home preparation is not 

 recommended. It is applied during the dormant period 

 of the tree, usually at the rate of one part of lime sulfur 

 to seven to ten of water. The exact amount of dilution 

 is determined by the use of the hydrometer. The material 



