12 REPORT OF SEARCH FOR ENEMIES OP CITRUS WHITE FLY. 



the upper half of the fruit (PI. III). It is in these places that the 

 development of the sooty mold is greatest. The mold may also be 

 found to a greater or less extent on the branches and underside of the 

 leaves. The injurious effect resulting from fungous growth on the 

 leaves is due to the check which it places on the assimilative process 

 that takes place within the tissues, retarding the availability of a 

 normal food supply for the tree. The injury to fruit has been care- 

 fully worked out by Drs. Morrill and Back/ and the following state- 

 ment is based on their investigations: The greatest injury by the white 

 fly lies in the reduction of the number, size, and quality of fruit pro- 

 duced. Conservative estimates, based on extended observations, have 

 placed the average yield in different white-fly infested groves in 

 Florida as between 20 and 50 per cent below that of normal unin- 

 fested groves. In addition to this the packing size of oranges is re- 

 duced one or two grades, while the increased number of culls due to 

 retarded ripening and other causes materially lowers the market 

 value of the crop. Moreover, fruit coated with sooty mold must be 

 washed before marketing. It has been shown by Dr. G. Harold 

 Powell,^ formerly of the Bureau of Plant Industry of this department, 

 that decay in shipment is greatly increased in washed fruit. Hence 

 the cost of washing, augmented by the additional loss from decay in 

 washed fruit over that which is unwashed, is an added loss from 

 white-fly infestation. 



Summing up the whole situation after their experience, Drs. 

 Morrill and Back estimate that in the average infested grove the 

 total loss from the white fly may be placed at about 45 to 50 per cent 

 of the value of the orange crop. Considering that fully 45 per cent 

 of the citrus groves in Florida are infested by the white fly it has been 

 estimated that in money value this would amount to more than half 

 a million dollars annually. 



Methods of Control and Their Efficiency. 



Greater effort has been devoted to the control of the white fly 

 than of any other pest in the Florida citrus belt. Agents of this 

 department commenced studying the white fly as early as the eighties, 

 and since 1906 this bureau has retamed a corps of investigators 

 continuously in the field testing the various possible methods toward 

 its successful control. Entomologists from the Florida State Experi- 

 ment Station have also been working along similar lines for many 

 years. The efforts of these different scientists have resulted in the 

 proposal of three distinct methods for control of the white fly: (1) 

 Fumigation with hydrocyanic-acid gas, (2) spraymg with various 

 insecticides, and (3) the utilization of several fungous diseases of 



» Bui. 92, Bur. Ent., U. S. Dept. Agr., 1911. 



« Bui. 123, Bur. Plant Industry, U. S. Dept. Agr., 1908. 



