72 HYDROCYANIC-ACID GAS FUMIGATION IN CALIFORNIA. 
the rays of light appear to have a direct effect in producing injury, 
these investigations have shown that this injury is intensified by the 
presence of heat, and the writer contends that burning during the 
daytime is directly attributable to heat as well as to the light itself. 
Fumigation should never be attempted in the daytime, even on 
cloudy days. Carry on the work at night and do not commence the 
operations until the sun has disappeared and the shades of darkness 
are approaching. Remove the last row of tents in the morning before 
the sun rises. 
WINDS. 
Fumigation should never be attempted during a heavy wind, for 
two reasons: First, the gas escapes out of the tent so that poor work 
results; second, injury to the trees might result. Dr. Morrill has 
called attention 1 to the variability of results on trees fumigated during 
a stiff breeze, stating that on different parts of the same tree he found 
the killing to vary from 30 to 100 per cent. 1 Observations made dur- 
ing this investigation cover instances in which the gas was driven 
from tents by winds in a very few minutes. The trees, of course, 
required a second treatment. The burning of trees fumigated during 
winds has frequently been observed. In light winds the injury 
appears to be more prevalent on that side of the tree from which the 
-wind comes. Heavy winds appear to produce the burning fully as 
much on the opposite side, or may affect the entire tree. A sudden 
change in temperature accompanying a wind appears to be especially 
severe in its results. Undoubtedly some of the cases of severe burn- 
ing during " electric" weather are due partly to the wind as well as 
to the heat. 
The author's experience has led to the conclusion that fumigation 
should never be carried on during a windstorm. As soon as a breeze 
arises sufficiently strong to "flap" the tents, it is well to discontinue 
work until calmer weather. 
INJURY TO SPRAYED TREES. 
Distillate oils are still used by a few orchardists in combating scale 
pests. As these men become discouraged with the oil treatment they 
adopt fumigation. In this connection it appears desirable to state 
a recent experience in the fumigation of trees previously sprayed with 
an oil combination spray. 
A lemon orchard of 40 acres was sprayed early in the autumn with 
a combination of Bordeaux mixture and distillate oil. Two months 
later about 25 acres of this orchard were fumigated partly with a Xo. 
1 and partly with a three-fourths schedule. Tins fumigation con- 
1 Bui. 76, Bur. Ent., U. S. Dept. Agr., p. 12, 1908. 
