BORAX AS A DISINFECTANT FOR CITRUS FRUIT 1 
By William R. Barger, Assistant Physiologist, and Lon A. Hawkins, Physi¬ 
ologist , Horticultural Investigations, Bureau of Plant Industry , United States 
Department of Agriculture 
The use of disinfectants in washing 
•citrus fruits has been a common prac¬ 
tice in California for many years. In 
1906 Smith 2 showed that the brown- 
rot of lemons caused by Pythiacystis 
citrophthora Smith and Smith, could be 
controlled by a solution of potassium 
permanganate, copper sulphate, or 
formalin in the wash water. Since then 
eopper sulphate has been used to a 
considerable extent commercially. For 
fifteen or twenty years hot water and 
soap have been employed in washing 
both oranges and lemons, and for the 
past ten years a soap containing borax 
has been extensively used. It has also 
been a common practice in some pack¬ 
ing houses to use a dilute solution of 
borax in the wash water in addition to 
the soap. Except in the case of brown- 
rot of lemons, there appears to be no 
data on the exact effect of these various 
disinfectants in the control of the 
fungous diseases of Citrus which gain 
entrance to the fruit in handling and 
harvesting operations and are partic¬ 
ularly evident during transit and on 
the market. 3 To obtain more exact 
information upon the possibilities of 
controlling some of the common Citrus 
parasites such as blue mold, caused by 
Penicillium italicum Wehmer, and 
green mold, caused by Penicillium 
digitatum Sacc., a series of experiments 
was conducted in which some common 
and cheap disinfectants were used in 
the wash water. Since the results of 
these investigations were fairly definite 
and present a basis for further com¬ 
mercial application of disinfectants in 
the control of certain Citrus diseases, a 
preliminary presentation is here given. 
The work was begun in California 
early in 1924, either Navel or Valencia 
oranges being used in all experiments 
described in this paper. In the first 
preliminary experiment, powdered boric 
acid U. S. P. and potassium alum Tech, 
were used. Navel oranges, which had 
been picked from four to six weeks, were 
prepared for the experiment by remov¬ 
ing thin slices of skin from each fruit. 
Seventy-five fruits were immersed for 
five minutes in a solution of 2.5 per 
cent of boric acid at a temperature of 
120° F.; two other lots of 75 each were 
treated, one by immersing in a solution 
of 4.5 per cent powdered alum and the 
other in hot water only for five minutes 
at 120° F. After the fruits had been 
removed from the baths they were 
inoculated with spores of blue mold ob¬ 
tained from a decayed fruit. The fruit 
was dried, packed, and stored in a room 
having a temperature of about 70° F. 
and a humidity of about 90 per cent. 
After one week both the fruit treated 
with hot water and that treated with 
powdered alum solution showed 100 per 
cent decay caused by blue mold. The 
lot treated with boric acid showed only 
2.5 per cent decay from blue mold and 
about the same percentage from green 
mold. Further holding of the lot 
showed some decay from what seemed 
to be Alternaria sp. or Pythiacystis sp. 
In this connection it is interesting to 
note that Smith 4 found that very 
dilute solutions of boric acid would not 
control Pythiacystis citrophtora on lem¬ 
ons. 
This experiment indicated that boric 
acid offered very promising possibili¬ 
ties and that alum was apparently of 
no particular value in concentrations 
such as could safely be used in wash¬ 
ing the fruit. Borax (technical grade) 
was later tested and found to be as 
effective as boric acid in controlling 
blue-mold decay, and, being much 
cheaper, was used in all later experi¬ 
ments. The investigation here de¬ 
scribed was concerned mainly with 
testing the efficiency of a 2.5 per cent 
solution of borax at various tempera¬ 
tures and with different methods of ap¬ 
plication in the control of blue and 
green mold which had been inoculated 
i Received for publication Aug. 31, 1924; issued April, 1925. 
a Smith, R. E., and others, the brown-rot of the lemon. Calif. Agr. Exp. Sta. Bui. 190, 72 p., illus. 
1907. 
3 Powell, G. H., and others, the decay of oranges while in transit from California. U. S. 
Dept. Agr., Bur. Plant Indus. Bui. 123, 79 p., illus. 1908. 
4 Smith, R. E. op. cit. 
Journal of Agricultural Research, 
Washington, D. C. 
( 189 ) 
Vol. XXX, No. 2 
Jan. 15, 1925 
Key No. G-372 
