Mar. 3,1923 
Further Studies of Corticium vagum on Potato 
765 
The plots used for the experiments in the two different years were 
separated by a distance of but a few rods; both were equally level, and 
the soil was uniform in structure and texture. Seed for the two seasons 
was obtained from the same stock which had been grown under com¬ 
parable conditions for a period of seven years on the farm on which the 
experiments were located. All tubers used for seed were selected with 
equal care each season for the uniform presence of the sclerotia of Corti- 
cium vagum. These were cut in halves and planted 5 inches deep at 
12-inch intervals in parallel rows 3% feet apart. The same method of 
taking observations was employed for the two seasons. 
In 1918, 22 rows were planted with 100 hills in each. The seed for 17 
of these rows was treated variously with mercuric-chlorid and formalde¬ 
hyde solution. The remaining 5 rows, placed at regular intervals through - 
out the plot, were planted with untreated seed for controls. Plantings 
were made on June 13 and 14. 
The first data from the 1918 experiments were taken on July 19, five 
weeks after planting. At this date a very striking difference appeared 
between the control rows and the rows grown from treated seed (PI. 1, C). 
The plants in the control rows were definitely undersized and irregular; 
“misses” were frequent, and many of the plants were just breaking soil, 
while plants in adjacent rows from treated seed were 10 inches or more in 
height (PI. 1, C). The examination of alternate plants in the various 
rows at this time showed severe stem lesions on 80 per cent of the plants 
from the untreated seed. Numerous primary, secondary, and even 
tertiary growing tips were destroyed, with total killing of the stems in 
many instances. The destructive attack on the secondary and tertiary 
stems is shown in the loss of 16 per cent of the stand and further by the 
fact that the number of stems per hill from the untreated seed was 
reduced over 26 per cent as compared with the number from treated 
seed. 
The final results obtained October 12 are equally definite in showing the 
severity of the disease during the season. Compared with the healthy 
plants the hills from untreated seed showed an average decrease in the 
number of tubers produced of 20.7 per cent with a corresponding 34.2 
per cent decrease in weight per hill. This average decrease in weight 
per hill, together with the 16 per cent loss in the stand, resulted in an 
aggregate loss to the crop from the untreated tubers of approximately 
50 per cent. 
Table III .—Comparative summary of the results obtained from the Plainfield, Wis., 
plots during the seasons igi8 and igig 1 
Year. 
Num¬ 
ber of 
rows. 
Num¬ 
ber of 
hills. 
Num¬ 
ber of 
control 
rows. 
Num¬ 
ber of 
control 
hills. 
Aver¬ 
age hills 
show¬ 
ing le¬ 
sions. 
Average 
decrease 
in stems 
per hill. 
Aver¬ 
age de¬ 
crease 
in 
stand. 
Aver¬ 
age de¬ 
crease 
in yield 
per hill. 
Aver¬ 
age de¬ 
crease 
in 
tubers 
per hill. 
Aver¬ 
age loss 
to crop. 
1018. 
22 
2, 200 
c 
500 
700 
Per 
cent. 
80. O 
Per cent. 
26. I 
Per 
cent. 
16. O 
Per 
cent. 
34.2 
12. 2 
Per 
cent. 
20. 7 
14*3 
Per 
cent. 
50.0 
15-4 
y . 
1919. 
35 
3)500 
0 
7 
75 -i 
f Slight 1 
(Increase.) 
2.8 
1 The figures in the table are obtained by comparing the plants grown from sclerotia-covered untreated 
seed with those growing from the same seed equally covered with sclerotia but treated variously with 
mercuric chlorid. 
