Mar. 15, 1924 
Wheat Scab y Corn Rootroty and Crop Successions 863 
This survey was made primarily for accurate information on the dis¬ 
tribution of wheat-scab, but notes were made also on a number of phases 
of the problem including the crop successions during the three previous 
years. As the same crop rotation usually is not followed on the different 
farms in any community, adjacent fields or fields close to each other were 
observed where wheat followed corn in some cases and in other cases 
followed other crops. 
Wherever wheat followed corn in the various States, perithecia of 
Gibberella saubinetii (Mont.) Sacc. were found in abundance on the old 
cornstalks and stubble left in the field. To make certain of their identity, 
specimens were sent to the laboratory at Madison, Wis., from each farm 
where observations were made. 
Table I gives a summary of the data collected in 1919. The difference 
between the percentage of heads scabbed when wheat followed corn as 
compared with the percentage when wheat followed some other crop is 
large enough in each State to be significant. A large number of wheat 
varieties are included in this summary. There is some varietal difference 
in the degree of susceptibility to scab, but the differences in respect to 
previous cropping are similar in all varieties and therefore all are sum¬ 
marized in one table. 
Scab also affects other cereals, including rye and oats, but generally the 
infection is of less extent than in wheat. Tabie I shows not only that 
wheat-scab infection is most severe when wheat follows corn, but that it 
also is greater when wheat follows wheat, rye, or oats than when it follows 
clover or timothy. The last two crops usually are not attacked by 
Gibberella saubinetii f the chief causal organism of scab of cereals, although 
Selby and Manns (ig) report a stem rot of clover produced probably by 
this parasite. Therefore, the disease is not so likely to be carried over 
from the previous year on the refuse from these two crops as on refuse 
from oats, wheat, and com. These data show that, over a large area, 
wheat scab occurs most abundantly where wheat follows corn. 
Table I .—Average percentages of wheat scab (head blight ) in igig following different 
crops in seven States 
State. ! 
| 
t 
Num¬ 
ber of 
coun¬ 
ties 
sur¬ 
veyed. 
j Average percentages of wheat scab after previous 
Num- | crop of— 
berof j 
neias 
sur* j 
veyed. i Corn. 
1 
1 
Wheat. 
Rye. 
Oats. 
Clover. 
Tim¬ 
othy. 
Tllinnic 
2 
| 
27 i 3 Q 
33 
23 
33 
22 
IO 
J 7 
47 ! IQ 
30 
16 
20 
. 
Towft . 
0 
/ 0 7 
27 71 
40 
3 ° 
Minnpsnts . 
y 
A 
20 j 66 
“7 
c8 
50 
43 
5 
Ohio. 
*T 
c 
D 
6 
11 
1 
17 
Tennpwp 
0 
c 
oy i Os! 
16 1 21 
4 
l 
9 
Wiornti^in . 
! D 
A 
101 14 
1 
5 
3 
T 
Average. 
| 
! 
i 
.; 43-3 
29. 2 
27. 0 
22. 7 
11. 4 
8.3 
SURVEY OF 1920 
The survey of 1920, as summarized in Table II, was confined to 
McLean County, Ill. All of the fields surveyed were on the same type of 
soil, in a more or less contiguous area, and all were sown with Turkey 
