388 THE MONTHLY BULLETIN. 



commonl}^ found. As high as 20 gallons of spray were used for a single 

 tree. 



RESULTS. 



Repeated examinations of the trees since the spraying was done have 

 been made, and also estimates of the total number of the insects killed 

 on badly infested trees. On April 15th, out of a total of 2,273 of the 

 insects examined, 2,238 were unmistakably dead, 31 were doubtful, and 

 4 were undoubtedly alive. The 31 doubtful specimens had grown none 

 since spray was applied in March, and might not develop into adults. 

 Granting that the 31 doubtful specimens would reach the adult stage, 

 the spraying resulted in killing 98^ per cent of the entire number of 

 larvffi and pupte present. Notwithstanding this high percentage of 

 killing, a considerable number of young larvffi may now be found on 

 leaves of trees where infestations were bad before spraying. 



EFFECT OF SPRAY UPON TREES. 



In the experimental work preliminary to the control spraying, there 

 was apparently no burning of foliage at the maximum strength of 10 

 per cent. The later spraying with 6 per cent miscible oil, which was 

 done just previous to the time of blooming of the trees, resulted in 

 almost total defoliation and more or less severe injury, especially in 

 cases where the spraying was done on a hot day. Spraying whenever 

 done in cool, cloudj^ weather did little if any harm to trees, though it 

 did drop considerable foliage. In one case where spraying was done on 

 March 16th, during a hot afternoon, practically all the leaves fell from 

 the trees. Later in the season as the new foliage began to push out 

 the black aphis (Aphis gossypii) , finding the condition of the succulent 

 growth very desirable, increased in abundance and gave the trees an 

 additional set-back and as a consequence much dead wood is now in 

 evidence. It is interesting to note that trees on this same property 

 that were sprayed in the early morning, while weather was cool and 

 damp, were injured only slightly, if at all. 



FUMIGATION. 

 It is now known that either spraying or fumigation will control the 

 white fly perfectly. There are places at Marysville today where fumiga- 

 tion work was done by Mr. G. E. Merrill, in 1911, that no white fly can 

 be found. Were it not for the difficulties and dangers attending fumi- 

 gation in a place such as Marysville, it would no doubt be the most 

 practical and effective means of control. 



SUMMARY. 



The white fly is present in Marysville but in most cases is not serious. 



Eradication was demonstrated to be impossible under the existent con- 

 ditions. 



As neither fruit nor trees are shipped from Marysville there would 

 seem to be little danger of the pest spreading to other citrus sections. 



It can be kept under perfect control by spraying with a miscible oil, 

 6 per cent strength, during the winter or early spring season. 



Such spraying may result in injury to trees, esgecially if done during 

 hot weather. 



Fumigation is a positive control measure, as demonstrated by the 

 State Horticultural Commission. 



