20 WHITE FLIES INJURIOUS TO CITRUS IX FLORIDA. 
well colored. The retardation of ripening, delaying as it does in some 
cases the time when the fruit is marketable and materially increasing 
the percentage of culls, causes injury which is very conservatively 
estimated to range from 2 to 5 per cent of the value of the crop. The 
injury to grapefruit in retardation of ripening by the citrus white fly 
is much less, varying from none at all to 2 or 3 per cent. 
Number and size. — The greatest injury by the white fly is in the 
reduction of the salable crop of fruit. Dr. Webber on this point 
makes the following statement: 1 
The effect of the sooty mold on the orange is very noticeable, the growth being 
usually greatly retarded and the blooming and fruiting light. In serious cases growth 
is frequently entirely checked, and blooming and fruiting wholly suppressed until 
relief is obtained. 
Prof. Gossard has estimated 2 that during a six-year period the 
reduction in yield due to the citrus white fly is from 25 to 40 per cent. 
Replies to a circular letter of inquiry addressed to orange growers 
and the observation of the authors in Florida indicate that the reduc- 
tion in yield due to the citrus white fly amounts to 50 per cent, on 
the average, when no artificial methods of control are practiced. 
From information received from many growers and from personal 
observation, the authors would estimate that with continued good care 
and with the additional fertilizer usually given infested trees the 
reduction in yield in different groves in a series of years amounts to 
an average between 20 and 50 per cent. 
The decrease in yield due to white-fly infestation ordinarily consists 
of a decrease in the actual number of fruit produced and also in the 
packing size. From information obtained it seems a conservative 
estimate to consider that oranges and tangerines are reduced either 
one or two packing sizes as a result of white-fly attack. For each 
packing size, the number of reduced fruit remaining the same, the 
reduction in the crop would average about 12.5 per cent. 
Expense of cleaning. — Fruit noticeably affected with sooty mold 
requires cleaning before marketing. One of the most economical 
machines for washing fruit used in Florida is a California washer used 
by Mr. F. D. Waite, of Palmetto, and Mr. F. L. Wills, of Sutherland. 
The cost of washing with these machines ranges from 1.4 to 2.5 cents 
per box. The cost of cleaning with the simplest machines is about 
5 cents per box. Mr. E. H. Walker, of Orlando, Fla., estimates the 
cost of hand cleaning oranges at 10 cents per box as a minimum and 
7 cents a box for cleaning grapefruit. In consideration of the fore- 
going it is estimated that the range in cost of cleaning the sooty 
mold from fruit to be from 1 to 10 per cent of the value of the crop. 
Shipping and keeping quality. — The sooty mold produced by the 
white fly and other citrus pests does not, so far as known, affect the 
1 Loc. cit., p. 9. 2 Bui. 67, Fla. Agr. Exp. Sta., p. 617. 
