IDEAL FERTILIZERS 73 



citrus whitefly, puncture the outside tissue and feed upon 

 the juices of the plant. Stomach poisons, therefore, are 

 of no avail. For their control we must depend upon con- 

 tact insecticides or fumigation. The principle of a con- 

 tact insecticide is to kill the insect by entering its breath- 

 ing pores, "spiracles," as they are called. The materials 

 most commonly used for this purpose are tobacco, soap, 

 or oil in some form. For the fumigation of ants, weevils, 

 etc., bisulphide of carbon is generally used. It is very 

 inflammable. 



The subject of fertilizing is too great to be discussed 

 in full here. A few plants seem to have no preference as 

 to the source of their food, while many are most suscepti 

 ble to the influence of different fertilizer materials. The 

 plant's welfare must be given first consideration, but 

 often we can combine fertilizing and insecticide effects 

 to good advantage. Commercial fertilizer is less in- 

 ducive to insect development than is stable manure, 

 some forms being far more active in this way than others. 

 Muriate of potash and kainit with their strong chlorine 

 content tend especially to lessen insect life in all forms, 

 and \vill do much to balance conditions made by the 

 use of stable manure; therefore they are to be preferred 

 to sulphate of potash for use in connection with it. 

 However, to have such material act as a direct insecti- 

 cide, as against cut-worms, etc., it is necessary to make 

 a heavy application on bare ground. At least 1000 

 pounds of kainit should be used per acre. This can 

 be put on after plowing and harrowed in, say, a month 



