Dec. 13, 1915 
Angular Leaf-Spot of Cucumbers 
475 
Some weeks later the experiment with copper sulphate was repeated. 
To liter quantities of distilled water in Jena flasks, chemically pure copper 
sulphate was added so as to obtain the following dilutions: 1 to 50,000; 
1 to 100,000; and 1 to 500,000. Some hours after full solution, 10 c. c. 
of each dilution were pipetted into sterile test tubes and to each was 
added a 3-mm. loop from a heavily clouded water suspension made from 
a 24-hour agar slant culture. From each of these tubes three plates 
were then poured at the end of 5 minutes, and again three more at the 
end of 10 minutes. As a check, a 3-mm. loop of the cloudy bacterial 
suspension was added to 10 c. c. of distilled water and from this tube 
three plates were also poured. The agar for the first set of poured plates 
was seeded with a 3-mm. loop from the dilution tube, that for the second 
set with a 2-mm. loop, and that for the third set with a needle dipped 
one-half inch into the fluid. The results in colonies are given in Table II, 
the counts being made on the sixth day. 
Table II .—Effect of copper sulphate on Bacterium lachrymans 
Number of colonies of Bacterium lachrymans developing in— 
Dilution used. 
Checks. 
1 to 50,000 copper 
sulphate. 
1 to 100,000 copper 
sulphate. 
1 to 500,000 copper 
sulphate. 
5-minute 
exposure. 
10-minute 
exposure. 
5-minute 
exposure. 
10-minute 
exposure. 
5-minute 
exposure. 
10-minute 
exposure. 
Plate 1 (3-mm. loop).. 
3 > 8 44 
78 
45 
118 
55 
3 > 4 12 
i. 75 6 
Plate 2 (2-mm. loop).. 
2, 296 
27 
16 
29 
44 
2,400 
9l6 
Plate 3 (needle). 
22 
0 
0 
0 
0 
12 
5 
SUMMARY 
(1) The angular leaf-spot of cucumbers is a widespread disease occur¬ 
ring in many of the Eastern and Middle Western States. 
(2) It is characterized by angular brown spots which tear or drop out 
when dry, giving to the leaves a ragged appearance. In the early stages 
a bacterial exudate collects in drops on the lower surface during the 
night and dries whitish. 
(3) Young stems and petioles may become soft-rotted or cracked open. 
(4) A virulent outbreak often materially reduces the crop by destroy¬ 
ing the needed active leaf surface. 
(5) The spot is caused by Bacterium lachrymans , n. sp., which enters 
through stomata, no wounds being necessary. This organism is quite 
different from the one described by Burger 1 in his papers on cucum¬ 
ber rot. No direct connection has been found between the leaf-spot 
and the soft-rots of the fruit. 
(6) Considering the results obtained in the laboratory with copper 
sulphate, it would seem that Bordeaux mixture properly applied is the 
remedy for this disease. Thorough field tests with it should at least be 
undertaken where the disease is troublesome. 
1 Burger, O. F. Op. cit. 
