FUMIGATION OF CITRUS TREES. 61 
used, to make sufficient allowance for the irregularity in the surface 
of the ground, which renders the possibility of leakage from under- 
neath greater than in regular orchard work. 
DOSAGES IN GENERAL FUMIGATION. 
If the treatment is for any one of the insects mentioned previously, 
the dosage recommended for that particular insect should be used. 
Frequently, however, two, or even three, different species may be 
found in the same grove. In such cases use that dosage which is 
heavy enough to destroy the most resistant one. For instance, if 
the purple and red scales, or the purple and black scales, occur in 
the same orchard use dosage schedule No. 1 for an exposure of one 
hour. If the red and black scales, or the yellow and black scales, 
occur simultaneously, use a three-fourths schedule for one hour, 
unless the black scale is in an advanced or matured stage, in which 
case a full No. 1 schedule is required. 
TIME OF THE YEAR FOR FUMIGATION. 
Although fumigation is carried on in California at all times of the 
year, there are certain periods in which the operations are more 
general. There are two main factors to be taken into consideration 
in fumigating, i. e., the species of scale insect and the condition of 
the tree. As to the latter, it may be said that at certain periods of 
the year the fruit is in such a tender condition that it can not with- 
stand a heavy dosage without injury. This period is while the fruit 
is of small size, usually from April until about August. The bulk of 
fumigation in California at the present time is carried on between the 
latter part of August and December. Probably the principal reason 
for treating during this period is that the black scale is usually at 
that time most successfully reached. Although the life history of 
the black scale has never been thoroughly worked out for the region 
in which these investigations were made, it is generally understood 
that the majority of the insects of the largest and most regular brood 
are hatched and in their least resistant stage during the months of 
September and October. In some favorable seasons the eggs are 
almost all hatched in August. 
The black scale occurs in practically every citrus-growing locality 
in southern California, while the purple, red, and yellow scales are 
more localized. Where any of these other species occur in orchards 
infested with the black scale it is a common practice to fumigate 
during the regular black-scale period, using the dosage necessary to 
destroy the most resistant species. The majority of these scale 
insects can thus be caught at one time. When fumigating for the 
purple scale alone, operations can be commenced as early in the 
season as the trees are in a condition to withstand the heavv dosage 
