ef 
17,4 Lee: Fungicides and the Citrus-canker Organism 333 
the lesser dilutions of Bordeaux 4—4—50 mixture, and then usually 
only for the longer periods of exposure. 
TABLE 8.—Results of exposures with 3-day-old culture of Pseudomonas 
citri in dilutions of Bordeaux 4-4-50 mixture." 
[Date of test, July 22, 1920; date of observation, July 25, 1920.] 
Dilution expressed in percentage. 
Exposure. 
10. | 20. | 30. | 40. | 50. | 60. | 70. | 80. | 90. | 100. 
Min. sec. 
2-00 4.--+ a I + + + + + + fs 
6 OO} + ~~ a + > “+ + - > + 
gat |i) Ns 3 zt = i 5 + sw atts Be ~ 
10 00); + ae + +5 = Geel a ae a gs = 
12 30; + + Se Rs ot, SP aa _ _ — 
15 00; + ae + as 1 ere Cease Pree ~ 
® Bordeaux 4-4-50 mixture was prepared as nearly as possible as it is done in the field. 
Commercial quicklime and copper sulphate were used. In order to avoid contamination of 
the tests, however, autoclaved tap water was used in making up the mixtures. 
b Tube tested for P. citri, July 24, 1920; positive, July 26, 1920. 
¢ Tube tested for P. citri, July 24, 1920; negative, July 26, 1920. 
Apparently the degree of impurities in the commercial lime 
and copper sulphate varies greatly and such variations are 
repeated in the toxic action of the Bordeaux mixture. In the 
eight tests made, Bordeaux 44-50 mixture, undiluted, at ex- 
posures of 15 or 20 minutes, resulted in the entire killing out of 
Pseudomonas citri. The tests indicate that in orchard practice 
the Bordeaux mixtures are far from being uniform in content 
and in bactericidal action. 
For orchard use against citrus canker this mixture has an 
advantage over the disinfectants previously listed, in that it 
adheres to the foliage even in the most violent rains, and pre- 
sumably affords some degree of bactericidal action as long as 
any of it is present on the leaf. Field tests in the Philippines 
and in Japan, as yet unpublished, support this statement. Bor- 
deaux 44-50 mixture would therefore seem to be more desirable 
than the other germicides previously listed for use as a disin- 
fectant spray in the eradication of citrus canker. Sterling * 
makes a similar statement of the action of Bordeaux mixture 
in Florida as follows: 
We have also noticed that where groves have been repeatedly sprayed 
with Bordeaux, even tho they are close to an affected grove, the chance of 
their becoming affected is considerably lessened, altho the Bordeaux does 
no good after the tree is once infected. 
‘Sterling, Frank, Eradication of citrus canker, Bull. Fla. Agr. Exp. 
Station 124 (1914) 53. 
