12 
FUMIGATION FOR THE CITRUS WHITE FLY. 
Wind. — The effect of wind upon the results is so marked that 
fumigation .should not be attempted with anything stronger than 
a slight breeze, particularly if the tents have not been rendered 
gas-tight or nearby so by the use of a "filler." It has been found, 
with an untreated tent, that with a dosage sufficient to destroy 100 
per cent of white fly pupae, a brisk breeze renders the results so 
uncertain that the effectiveness may be as low as 30 per cent in 
some sections of the tree, while in others the destruction of the 
insect may be complete. 
Atmospheric humidity and dews. — The presence of moisture in the 
form of dew does not seem to have any deleterious effect upon the 
foliage, although in California it is generally considered necessary to 
materially increase the dosage in such cases to insure the effective- 
ness of the work against scale insects. Prof. H. A. Gossard a con- 
cluded that "moisture did not seem to interfere with the efficiency 
of the work, unless the leaves were almost dripping, when it became 
a factor of much disturbance, though not as great as we had thought 
probable." 
The experiments conducted by the writer and assistants during 
January and February, 1907, show that moisture on the foliage 
during the period of exposure has no marked effect on the foliage 
or upon the efficiency of the gas against the white fly. In the six 
instances where the leaves were wet with dew, examination showed 
that 100 per cent of the insects were destroyed in* aU cases but one, 
and in tins only a single specimen out of 102 under observation, 
before and after fumigation, survived the treatment. 
The results of the tests concerning the effect of atmospheric 
moisture on the efficiencv of the fumigation treatment are oriven in 
Table I. 
Table I. — Effect of atmospheric moisturi on efficiency of fumigation. 
Experi- 
ment 
No. b 
Air 
humidity. 
C end it ir.n- Cc.idition 
of tent. of leaves. 
Per cent 
of insects 
killed. 
Amount 
of evanid 
Amount 
recom- 
of cvaiiid 
mended in 
used. 
tallies: -In 
minutes 
exposure. 
Ounces. 
Ounces. 
30 
24 
32 
27 
I5f 
14 
9 
11 
13| 
18 
33* 
32 
36* 
34 
28 
19 
22 
26$ 
27 
26* 
30.7 
40.2 
4.5.12 
45.21 
15.22 
45.25 
4.5.27 
.50.2 
60.2 
60.19 
Per cent. 
100 
94+ 
100 
87 
s7 
96 
100 
97 
64 
Wet 
. Wet 
. Moist 
Wet.... 
Damp. . 
.. Wet 
Damp.. 
Damp.. 
Wet 
. M list 
. Wet 
. Moist 
Damp. . 
Damp. . 
. Drv 
. Dry 
100 
100 
100 
100 
99. 
100 
100 
100 
a Bui. 67, Fla. Agr. Exp. Sta., pp. 647-648. 
b The number preceding the decimal point indicates the length of exposure. 
