196 Nature-Study Agriculture 



Sprays Many of the sucking insects have softer bodies than 



the biting insects usually have, which makes it the easier 



external to kill them with contact poisons. This is especially 

 true of the many kinds of plant lice. The sprays used 

 for such insects may be either of a kind that will kill 

 by poisoning through the soft skin of the insect, or by 

 shutting up the breathing pores (spiracles). Tobacco 

 extract will kill by poisoning through the skin. A mix- 

 ture containing kerosene (kerosene emulsion) will close 

 the breathing pores (Fig. 150). 



Kerosene Oil will not dissolve in water, but if oil and water are 



shaken up together the oil breaks into very fine drops 

 which remain for a little while floating all through the 

 water. Such a mixture of oil and water is called an 

 " emulsion." If a little dissolved soap is added, the 

 emulsion will be much more perfect and the oil and water 



Recipe will not separate so readily. A good recipe for making 

 kerosene emulsion is as follows : Dissolve a one-inch 

 cube of laundry soap in a pint of hot water. Remove 

 from fire and add one pint of kerosene. Churn with egg 

 beater. For trees or plants in foliage dilute this mixture 

 with three gallons of water. For dormant trees without 

 leaves dilute with only one gallon of water. (Exp. 2.) 

 Such a spray is used for killing plant lice and scale insects. 

 Just before being used it should be thoroughly mixed by 

 putting the nozzle of the spray pump into the bucket or 

 barrel and pumping the mixture through until it is creamy. 



Soap- A simple spray that will kill scale insects is made by 



spray dissolving one pound of soap powder in five gallons of 



water. This solution should not be used on tender 

 plants, as it may burn the foliage. 



