INSECT ENEMIES AND THEIR CONTROL 105 



of insects and diseases affecting greenhouse crops. See 

 Chapter VI. 



Tobacco fumigation. It is undesirable to use spray 

 materials as generally in the greenhouse as in the 

 management of crops grown out of doors. It is possible 

 to employ in inclosed structures methods that are im- 

 practicable in the open ground. Fumigation has been 

 practiced for many years in controlling the ravages of 

 certain insects, especially aphids and the white fly. The 

 poisonous alkaloids of tobacco are especially destructive 

 to the various species of aphids or plant lice. 



Fumigation by the burning of tobacco stems is the 

 most common method of combating plant lice in the 

 large vegetable-forcing establshments. The stems, 

 which are mostly the mid-veins of tobacco leaves, should 

 be as fresh as possible in order to make an effective 

 smudge. They can often be obtained at slight cost from 

 local cigar factories. They vary considerably in strength, 

 due to age and possibly to different varieties, and this 

 factor should be kept in mind when stems are procured 

 from different sources. 



The stems should be dipped in water or sprinkled, so 

 that they will be moist when the smudge is started. A 

 convenient way is to place the stems in old burlap bags, 

 kept for the purpose, and to plunge them into a tub or 

 a tank of water. After the surplus water has been 

 drained off, the stems are ready for the fire and the bags 

 will be found convenient for carrying them through the 

 houses. Many greenhouse men simply sprinkle the 

 stems a few hours before they are wanted for use. It is 

 possible to make them too wet to burn, especially if they 

 have been stored in a moist place. 



Some growers make the smudge immediately after 

 daylight, but the most common practice is to attend to 

 this operation in the evening, when it will not interfere 

 with regular work in the houses. 



