12 KEPOKT OF SEARCH FOR ENEMIES OF CITRUS WHITE FLY. 
the upper half of the fruit (PL 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, 1 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, 2 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 
W,hite-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 retained 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) spraying with various 
insecticides, and (3) the utilization of several fungous diseases of 
i Bui. 92, Bur. Ent., U. S. Dept. Agr., 1911. 
» Bui. 123, Bur. Plant Industry, U. S. Dept. Agr., 1908. 
