te 
17,4 Lee: Fungicides and the Citrus-canker Organism 331 
to formalin burning, and a dilution of 1 to 120 was the strongest 
practicable without causing severe burning. The use of for- 
malin as a spray in orchard work against citrus canker hardly 
seems feasible, therefore, unless in remote cases it is desirable to 
remove the leaves of the tree. 
TABLE 6.—Results of exposures with 3-day-old culture of Pseudomonas 
citri in dilutions of lime-sulphur solution." 
[Date of test, February 7, 1920; date of observation, February 9, 1920.] 
Dilution. 
Exposure. z S S s s g g g g 
ee ee ee pe oa ee eee oe 
8 B} 8 8 8 8 8 8 8 3 
ts J we Son mw me Se | we mt Son we 
Min. sec. 
i> |e ae ee =} - + + - + ae 
6 00; + + ss & x = > mi + —_ - 
ER Bs bao ws + + 4+ oie 25 = oe Bae ~ _ 
10 00; + a + ay + aE 38 + oy —_ 
12. 30) + + + 25 + nye i + ~— _ 
15 00; + Bs a3 eB + a 8 + | e+ _ _ 
4 The stock solution of lime sulphur employed had a density of 32° Beaumé. 
b Tube tested for P. citri, February 11; positive, February 13. 
¢ Tube tested for P. citri, February 9; positive, February 11. 
Two preliminary tests were necessary with this fungicide in 
order to obtain the limits of its action against the canker bacteria. 
Table 6 gives the results of the third test. Two later tests to 
define more. closely the action of lime-sulphur solution were not 
in close agreement. The fourth test showed a dilution of 1 
to 1,500 killing the canker bacteria at all exposures, while the 
1 to 1,750 gave such results only in the longer exposures of 124 
and 15 minutes. The fifth test showed dilutions of 1 to 1,250 
and 1 to 1,500 to be positive at all periods of exposure; 1 to 
1,000 was negative at all periods of exposure. It seems safe 
to regard a dilution of 1 to 1,000 lime sulphur as sufficiently 
strong to kill the canker bacteria in the absence of organic 
matter. 
The use of lime sulphur in orchard practice is especially de- 
sirable, of course, because of its additional value against citrus 
scab, wither tip, and insects. It would seem much more de- 
sirable than formalin; the latter has been used extensively 
against canker in the past, and its use hardly seems warranted 
by these tests and the writer’s field experience. 
