30 
The duration of the treatment indicated in the second table varies 
with the size of the tree, but in general at least forty minutes should 
be allowed. 
In Florida fumigation for the white fly can be successfully prac- 
ticed only during the short period in winter when the insect. does 
not occur in the winged stage. This period covers from two and a 
half to three months, namely, December, January, and February, 
varying with the climatic conditions of different years. This is the 
dry season for Florida, and the trees are in a dormant condition, 
with the leafage well matured and hardened, and it is possible to 
apply a greater strength than would be safe under California condi- 
tions. The strength recommended is approximately the same as for 
deciduous nursery stock, viz, 1 ounce of cyanide to 100-115 cubic feet 
of space, with a duration of 40 minutes. 
General directions.—In the fumigation of growing stock, citrus or 
other, the treatment consists in inclosing the tree with a tent and 
filling the latter with poisonous fumes generated in the same way as 
described for nursery stock except that less of the chemicals is used. 
The treatment is made at night for trees in foliage, which includes 
all work in citrus orchards, to avoid the much greater likelihood of 
injury to tender foliage in the sunlight. The vessels for setting off 
the charges of cyanide and acid may be, for small doses, any ordinary 
earthenware jars. For large trees requiring heavy doses, tall wooden 
pails have proved more satisfactory, two generators being employed 
for the very largest trees. 
It is important that the water be put in the vessel first, then the 
acid, and lastly the cyanide. If the water and cyanide are put in 
the vessel first and the acid poured in afterwards, there is danger of an 
explosion which will scatter the acid and burn the tents and the oper- — 
ator. In the spring, when the trees are tender with new growth, and 
in early fall when the oranges are nearly grown and the skins are 
likely to be easily marred, and also with young trees, it is advisable 
to add one-third more water than ordinarily used, or to add the 
cyanide in larger lumps. This causes the gas to generate more slowly 
and with less heat, and, if the tents are left over the trees a third 
longer, the effectiveness of the treatment will not be lessened. The 
person handling the chemicals should always have an attendant with 
a lantern, to hold up the tent and enable the cyanide to be quickly 
dropped into the generator, and to facilitate the prompt exit of the 
operator. 
Trees are fumigated for the black scale in southern California in 
October, or preferably in November. The red and other scales may 
be treated with gas at any time, but preferably at the season already 
indicated. In California most of the work is done by contract, or 
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