120 
Directions as to the quantity or strength to be used accompany 
all these preparations, but the grower, after experiment, must 
himself finally determine the matter, since no two greenhouses 
are alike in regard to tightness. 
The method of fumigation with tobacco stems in common 
practice is to use 3 piles of stems, of about half a bushel each, 
to every 100 linear feet of space, dampening the pile to prevent 
rapid burning. This is done in the evening, and the fire is ap¬ 
plied when leaving the building for the night, the house being 
kept as tightly closed as possible until morning. 
If the infested plants are few, or are out-of-doors, a spray 
of whale-oil or “ivory" soap or one of the liquid nicotine extracts 
may be used. The quantity of diluent for the latter recommended 
by the manufacturers must of course be modified if houses are 
exceptionally loose or tight in construction. The soap solutions 
are prepared by dissolving 1 pound of the soap in 6 to 8 gallons 
of water, and the application should be made with a bucket- or 
small barrel- sprayer. A hand syringe may be used, but the large’* 
apparatus has a more even and a stronger pressure, and is the 
most economical in the end. 
In spraying the fluids above mentioned it should be remem¬ 
bered that they kill only by coming in contact with the insect, and 
it is therefore essential that the spraying be thoro. It is also im¬ 
portant to begin treatment, whether it be spraying or fumigation, 
as soon as the lice make their appearance, not waiting until they 
begin to do noticeable damage, since they are then much more 
difficult to control. 
( b ) Root Forms 
In Illinois but one root aphis, commonly known as the corn 
root-aphis, Aphis maidiradicis Forbes (Fig. 32, 33), has been 
found damaging cultivated flowering plants, and of these only the 
aster is seriously injured. Asters sometimes make little or no 
noticeable growth, turn yellow and sickly, and easily succumb to 
the midday sun. Usually plants showing these symptoms are be¬ 
ing attacked by root-lice, and upon examining the roots man-y small 
bluish-green lice, about the size of a pin-head, will be found.* 
Again, the lice are attended by ants, and the presence of their 
nests close to the plants is good evidence that aphids are also 
present. 
The life history of these aphids differs little from that of the 
aerial forms except as modified by the fostering care of the ants, 
*Plants attacked by the common white-grubs show similar symptoms, but 
the wilting and dying of the plant is usually very sudden. If white-grubs 
are present the roots will be cut off, and a large grub will be found near 
them. 
