64 HYDROCYANIC-ACID GAS FUMIGATION IN CALIFORNIA. 



with these different dosages were about the same. The very young 

 insects were destroyed, but a large proportion of the matured ones 

 and eggs escaped. A few trees were then covered with double tents 

 (two tents, one over the other) in order to render them tighter and 

 twice schedule No. 1 was used. An examination of these results a few 

 days after treatment showed eradication on some trees, while others 

 contained a small percentage of live adult insects. A 10-acre block 

 of trees was then fumigated with double tents (two tents, one over 

 the other) and twice schedule No. 1. An examination of this work 

 showed a considerable percentage of live matured insects and eggs. 



From the results of the aforementioned fumigation against the 

 mealy bug it is seen that the early stages of this insect are destroyed 

 by the use of twice dosage schedule No. 1. If a study of the life 

 history should reveal that at some certain time they may all be 

 found in this early stage of development fumigation might then prove 

 of some avail. The failure, however, to secure eradication of the 

 mealy-bug in its more mature stages, even where dosages as high as 

 three times schedule No. 1 were used, indicates that general com- 

 mercial fumigation for the mealy bug is impractical. 1 



FUMIGATION DURING THE BLOSSOMING PERIOD. 



The statements by experts on fumigation as to the amount of 

 injury resulting from work while the trees are in blossom are very 

 conflicting. Some fumigators hold that a very light dosage will 

 destroy tender blossoms, while others believe that the blossoms will 

 stand a heavy dosage. In order to decide this point, much experi- 

 mentation has been carried on and many observations made through- 

 out this investigation. To attempt to relate the details of the scores 

 of experiments and observations made along this line in all parts of 

 southern California would require too much space, so mention will 

 be made here only of general results. Fumigation observations by 

 the writer have covered the entire period from the time the blossoms 

 first appear until the petals drop. In not a single instance during this 

 period has any serious injury resulted even though dosages as high as 

 1J and 2 times schedule No. 1 have sometimes been used. 



Occasionally some blossoms were affected, and dropped off soon 

 after the treatment, yet these blossoms were normally weak and 

 would have fallen without fumigation. The fumigation merely 

 hastened their shedding. Even if a heavy shedding took place 

 (which never happens), there would be no cause for alarm, as the 

 setting of only a small percentage of the blossoms on a citrus tree is 

 necessary to produce a full crop of fruit. 



1 This same conclusion has been reached by Mr. E. O. Essig, horticultural commissioner of Ventura 

 County. (See Pomona College, Journal ol Entomology, December, 1909.) 



