SUMMER MEETING. 31 



from six inches to one foot, according to the size of the tree and the 

 condition of the soil. 



Carbon bisulphide can be purchased in bulk for 10 cents })er 

 pound, and, if used as above directed, it will cost ll cents for the 

 material to treat one tree. It must be understood, however, that the 

 carbon bisulphide only kills those aphids that are there at the time 

 the injection is made ; its work is done in a short time, and the fumes 

 soon disappear, and there is then no reason why other colonies should 

 not establish themselves on these same roots. To prevent this, one 

 should apply, as above directed, about two pounds of tobacco dust 

 to each tree either just before or within a few days after the injection 

 of the carbon bisulphide. 



The use of the carbon bisulphide is not advised except in bearing 

 orchards or in extreme cases such as where the trees are very badly 

 infested and it is very desirable to kill the aphis at once. The use of 

 tobacco dust is always necessary in order to prevent the aphids from 

 again establishing themselves, and since this is the case, it is no more 

 trouble to apply a larger quantity of tobacco dust and kill the aphis 

 all with one operation. The tobacco dust works slower than the 

 carbon bisulphide, but it not only kills the aphids, but it also remains 

 about the tree, and prevents other colonies from forming. It costs 

 from 3 to 5 cents per tree to kill the aphids by means of tobacco dust, 

 but it will cost only about one-half that amount each succeeding year 

 to keep them away. If we take into account the cost of the material 

 and the trouble of making the injection of carbon bisulphide and the 

 cost of the tobacco and trouble of applying in order to keep the aphis 

 away, we shall find that the cost and trouble of applying only the 

 tobacco dust in the beginning is about the same. Hence I would 

 advise the use of finely powdered tobacco or tobacco dust as a means 

 of killing the root inhabiting form of the wooly-aphis on apple trees, 

 and would urge its use every spring as a preventive. Always apply 

 the tobacco dust, as above directed, by removing the earth from 

 around the trunk of the tree for a distance of 2 feet and from 4 to 

 6 inches in depth, and evenly distribute the tobacco in this excava- 

 tion, taking care to place it close to the trunk also, and then cover 

 it with the earth. 



Judging from the experiments above described, it is believed that 

 the liberal supply of tobacco dust, applied as stated, will cheaply and 

 effectually kill and hold in check the wooly-aphis and prevent serious 

 injury from this pest. The experiments with tobacco dust as a means 

 of controlling this insect will be continued for several years by using a 



