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 . a 
TDate of test, February 7, 1920 ; date of observation, February 9, 1920.] 
Dilution. 
Exposure. 
1 to 500,000. 
1 to 200,000. 
1 to 100,000. 
1 to 60,000. 
1 to 20,000. 
I 
1 to 10,000. 
1 to 5,000. 
1 to 2,000. 
1 to 1,000. 
1 to 600. 
Min. 
2 
sec. 
30 
+ 
+ 
+ 
+ 
+ 
+ 
-k 
6 
00 
+ 
+ 
+ 
4 - 
+ 
+ 
+ 
4 
— 
— 
7 
30 
+ 
+ 
+ 
+ 
+ 
4 
4 
b + 
- 
— 
10 
00 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
— 
— 
12 
30 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
— 
— 
15 
00 
+ 
+ 
+ 
+ 
+ 
+ 
4 
= 4 
— 
— 
* The stock solution of lime sulphur employed had a density of 32° Beaume. 
b Tube tested for P. citri, February 11 ; positive, February 13. 
c 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 12 ^ 
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. 
