52 FUMIGATION INVESTIGATIONS IN CALIFORNIA. 
Experiment No. 3. — On July 11 and 13, four Valencia orange trees 
were fumigated, using a lj-ounce dosage rate, 4 trees receiving a 
H -ounce dosage, 8 trees a l§-ounce dosage, and 4 trees a 2-ounce 
dosage. These trees were in a perfectly normal condition, about 
7 to 8 feet high, and contained young fruits fully three-fourths of an 
inch in diameter. With the lj-ounce dosage rate no fruit was 
burned; with the H-ounce rate an occasional orange was slight ly 
burned; with the 1 |-ounce rate 1 a very small percentage was burned, 
while with the 2-ounce rate a considerable percentage was injured. 
This demonstrates that a 2-ounce dosage rate could not be safely 
used on trees of this size. 
Experiment No. 4- — During the middle of July a large number of 
orange trees of all sizes were fumigated at Santa Fe Springs, CaL, 
using various dosage rates. The trees fumigated were of several 
varieties, in a healthy condition, and all well filled with fruits about 
the size of an English walnut and slightly larger. It was found from 
this experiment that a dosage rate of 1 ounce to 100 cubic feet could 
at this time be used without injury on orange trees 15 to 16 feet high. 
Only an occasional orange was burned by l\ ounces. Smaller trees 
proved able to stand a heavier dosage than larger ones without 
appreciable injury. 
On the basis of information obtained from experiment No. 4, 
dosage schedule 1 (p. 65) was prepared. This schedule was put into 
use during the latter part of July and has been in use, up to the 
time of writing, by two outfits, at Whittier, Cal. Although no 
noticeable injury to the fruit has resulted from the use of this dosage, 
the general effect on the tree has indicated that a heavier dosage 
could not have been used with safety. 
A further example of the tender nature of small fruits was shown 
in some work done by an excellent fumigator at Downey, Cal., during 
the latter part of May. The fruits were for the most part three- 
eighths of an inch or less in size, while the trees were thoroughly 
infested with scale and in a generally unhealthy condition. So far 
as could be determined, a dosage rate of approximately three-fourths 
to 1 ounce was used. The larger percentage of the fruits on these 
trees was burned. Other instances of like fumigation, where the 
fruits were one-fourth inch or less in diameter, have been seen. The 
fruit at this period is very tender. Doubtless it is the most critical 
period of any during which fumigation is conducted. 
From the foregoing, it is evident that heavy dosage can not be 
used while the fruits are small without more or less injury, and that 
the most critical period during which fumigation may he conducted 
is between the time when the fruits are set and the time when they 
attain the size of a walnut. 
