66 HYDROCYANIC-ACID GAS FUMIGATION IN CALIFORNIA. 
resistant. As all three kinds of citrus are fumigated at the same 
time, regardless of kind, it is necessary to base advice on the one most 
susceptible to injury. If the tenderest kinds escape injury the more 
resistant very naturally will do so. Hence, in reality the recommen- 
dations in this bulletin are based on the orange, partly because of its 
greater acreage but mainly because any recommendations made for 
it will apply equally to the grapefruit or lemon. 
The lemon blossoms throughout the }~ear in California, so that 
different sized fruit may be found at all times. This is very different 
from the orange, which has one regular crop. Lemons usually will 
escape pitting or burning under conditions which might seriously 
injure oranges. This allows a wider range of activity in fumigating 
lemon trees. The work can be continued somewhat later in the 
spring and commence earlier in the summer than with the orange. 
In fumigating a section containing lemon and orange trees it is good 
policy, where convenient, to commence on the lemons, leaving the 
oranges until a later period. 
EFFECTS OF FUMIGATION ON UNHEALTHY TREES. 
Unhealthy citrus trees are found universally. Occasionally a 
part or whole of an orchard is composed of trees weakened by lack of 
such essential treatment as ^proper cultivation, fertilization, or irri- 
gation. Many orchards contain trees weakened from attacks of a 
gum disease, of " gophers" (ground squirrels), scale insect pests, 
and numerous other causes which check their normal development. 
These unhealthy trees are less resistant to injury from fumigation 
than perfectly healthy ones. In examining results hi an orchard 
recently fumigated the writer has noticed frequently that the fruit 
on a few trees that had been weakened by disease was severely pitted 
or burned, while that on all healthy trees was uninjured. A heavy 
dropping of fruit might have taken place in the unhealthy trees, while 
the others were unaffected in any way. A most striking example 
of severe injury to unhealthy trees was seen in an orchard fumigated 
with double tents (one tent over the other) using a dosage twice 
schedule No. 1. Healthy trees in some cases were severely burned 
back at the top for about a foot, accompanied by the dropping of 
some leaves, while the trees weakened by gum disease usually would 
be burned back from 2 to 3 feet and drop practically all their leaves. 
Severe injury to unhealthy trees has been seen even where the 
three-fourths schedule was used. 
Practical fumigators have always been aware of the susceptibility 
of weakened trees to injury and have decreased their dosage greatly 
in treating such trees. The grower should not complain if the fruit 
and leaves on their unhealthy trees are slightly injured. Such fruit 
is normally of the inferior grades, while the damage caused by the 
