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. 
