260 Practical Orcharding On Rough Lands. 



Now that we have found such a vast differ- 

 ence in the way in which the insects take their 

 food, we find that we must also use two kinds 

 of insecticides. For instance in order to pro- 

 tect against chewing insects we cover the por- 

 tions which are likely to be attacked with some 

 poison, arsenate of lead being the most ef- 

 fective. But when attempting to protect against 

 those which suck the sap from bark or leaf we 

 find that poisons are not effective, so we have 

 to use something which will kill by coming in 

 contact with the insect; we call these, such as 

 oil, soap, tobacco ooze, lime-sulphur, etc., con- 

 tact insecticides. Air slaked lime and fine road 

 dust are frequently used for the destruction of 

 plant lice, as they kill them by stopping up the 

 pores in their bodies through which they 

 breathe, and these are also contact insecticides. 

 We shall leave the exact time of making the 

 various applications and the strength to use 

 to be gotten by reference to the Bulletins and 

 Spray Calendars to which we have already re- 

 ferred. 



Appliances. — After having decided that 

 spraying is absolutely necessary in order to 

 succeed and that it must be done promptly as 

 a means of protection; also that the proper 

 material must be used in a most thorough man- 



