12 
For the same reason about fifteen days should be allowed after treat- 
‘ ment before cultivation is resumed. If the soil is either very wet or 
very dry, treatment should be withheld. To be in the most favorable 
condition for treatment, the soil should be quite moist and moderately 
permeable, with a firm, even surface, well compacted by rain and hay- 
ing a depth of at least 8 inches. . 
Extent of diffusion—The extent of diffusion of the vapor determines 
the distance apart at which the injections must be made in order to 
reach all parts of the soil evenly and effectively. This varies considera- 
bly with the amount of the dose, the temperature and humidity of the 
soil, and other conditions. It has been found more satisfactory to 
employ smaller and more frequent doses rather than a few large ones. 
A dose of 5 or 6 grams (4 to $ ounce) is believed to be thoroughly 
effective through a radius of from 12 to 20 inches, though it may pene- 
trate much farther than that. The general rule is to make 3 injections 
per square meter (1f square yards, nearly) in light soils and 4 injec- 
tions in heavy soils. The arrangement of the holes must necessarily 
vary more or less, according to the system of planting. They should 
be at regular intervals, however, so as to cover the ground evenly, 
and never nearer than 1 foot to the base of the vine. It must be 
remembered that to be effective all the ground must be treated, and 
not merely those places where the presence of the enemy is proven by 
its injuries. 
Repeated treatment.—On account of the liability of injuring the vines 
it has been found best to make the treatment in two small applications, 
separated by an interval of from six to ten days. This decreases the 
density of the vapor, but continues its action for a much longer time. 
It removes the danger of injuring the vines, and gives even better 
results upon the insects than would be obtained by one large dose. 
The total amount of carbon bisulphid to be used should be divided 
into as many equal parts as there are injections to be made. The holes 
for the second treatment should be intermediate between those for the 
first. . 
Depth of the holes.—The depth of the holes depends somewhat upon 
the depth and permeability of the soil, the average depth being about 
1 foot. A depth of 16 inches is desirable upon deep or very permeable 
soil. 
Season of application Treatment may be applied at any season of 
the year; but, as it is followed by a slight check in growth, it should 
not be applied either at the flowering or fruiting season, as the check 
would injure the crop most at those seasons. The injury to the vines 
results from the killing of the tender, fibrous, feeding roots. It 
would therefore be better to apply the treatment before these roots 
have started much—that is, early in spring—or after they have become 
hardened that is, after fruitage in the fall. The condition of the soil 
usually favors the spring treatment, and the condition of the insect is 
