762 
Journal of Agricultural Research 
Vol. XXII 1 , No. 9 
The relative value of these data as an index to the pathogenic action 
of the fungus under natural conditions of potato culture in Wisconsin 
was indicated in field studies conducted at Madison and Plainfield. 
SOIL INOCULATION WORK AT MADISON, WIS. 
During the season of 1919 four successive plantings of Irish Cobbler 
potatoes were made at approximately 10-day intervals in soil inoculated 
with the sterile mycelium of Corticium vagum . In the process of plant¬ 
ing, a pure culture of the fungus grown on a sand-commeal medium for 
four weeks was placed in the soil and two one-half tubers, disinfected 
before cutting, were planted directly above but in contact with the cul¬ 
ture. All sets were then covered to a depth of approximately 6 inches. 
One plant was grown in uninoculated soil, as a control, for every two 
plants grown in inoculated soil. In order to obtain an adequate range 
of soil temperature the first crop was planted at the early date of April 
26. The additional successive plantings were made in parallel rows at 
the various dates of May 7, May 17, and May 30. Observations on the 
plants in each row were made approximately six weeks after planting. 
The results of these observations are recorded in Table I. A thermo¬ 
graph record was kept of the soil temperature at a depth of 2 inches 4 
for the months of May and June. These temperatures, together with 
the daily precipitation for the same two months, are recorded in Table II. 
Table I .—Effects of Corticium vagum on potato crops planted at various dates through 
April and May 
Date of planting. 
Total 
hills 
har¬ 
vested. 
Total 
stems 
exam¬ 
ined. 
Stems slightly 
injured. 
Stems severely 
injured. 
Growing tips 
destroyed. 
Total 
stems 
in¬ 
jured. 
Num¬ 
Per 
Num¬ 
Per 
Num¬ 
Per 
Per 
ber. 
cent. 
ber. 
cent. 
ber. 
cent. 
cent. 
Apr. 26. 
32 
182 
17 
9-3 
27 
14. 8 
47 
25.8 
50.0 
May 7. 
27 
202 
14 
6.9 
47 
23.2 
52 
25-5 
56.0 
17 . 
21 
118 
19 
16.1 
14 
11. 8 
8 
6.7 
34.7 
30 . 
25 
108 
33 
30.5 
26 
24. 0 
6 
5-5 
60. O 
The result of the experiment shows no specific correlation between 
the time of planting and the percentage of stems showing injury; on 
the other hand, the type and intensity of injuries produced by the 
fungus are evidently very closely related to the date at which plantings 
were made. As shown in Table I the plants grown from the tubers 
planted April 26 to May 7 exhibited a high percentage of growing-point 
destruction as well as a large number of stems which were severely 
injured. In comparison, the stems grown from the tubers planted on 
the two later dates of May 17 and May 30 were largely free from growing- 
point injury and on the whole exhibited lesions considerably less severe 
than those shown on the plants of the two earlier crops. 
A more striking feature of the experiment was noted in the fact that 
the secondary stems which grew later from the seriously injured primary 
4 Thermograph records of the soil temperature were also kept at a depth of 4 inches for the first two weeks 
of May. A comparison of the mean daily temperature at the depths of 2 and 4 inches showed an average 
daily difference for the period of 2.2 0 C. The daily mean temperatures at 4 inches after May 19 are calcu¬ 
lated by subtracting 2.2 0 from the daily mean at 2 inches. The results are recorded in Table II. 
