864 
Journal of Agricultural Research voi.xxvii.no. n 
wheat. While only a small wheat acreage was surveyed as compared 
with that of the previous year, the conditions under which the crop was 
grown were very much more uniform, so that in many ways the data are 
more significant than those obtained in 1919. 
Table II .—Percentages of scab (head blight) in Turkey wheat following different crops, 
in McLean County, III., in 1Q20 
Field 
Num¬ 
ber. 
Size 
of 
field. 
Previous 
crop. 
Percentages of scab at different locations in.fields. 
Grand 
average 
follow¬ 
ing 
each 
crop. 
1 
2 
3 
4 
5 
6 
7 
8 
9 
10 
11 
12 
Av¬ 
er¬ 
age. 
Per 
Per 
Per 
Per 
Per 
Per 
Per 
Per 
Per 
Per 
Per 
Per 
Per 
Per 
Acres. 
cent. 
cent. 
cent. 
cent. 
cent. 
cent. 
cent. 
cent. 
cent. 
cent. 
cent. 
cent. 
cent. 
cent. 
107 
So 
Com . . 
6.0 
IO- 0 
A- O 
5* 0 
2* O 
3* 0 
6* 0 
5* O 
5.1 
) 
a 7 q 
do 
8.0 
3.0 
3. O 
10- 0 
2- O 
2* 0 
5- 0 
4.7 
473 
! 
IO 
2.0 
A- O 
2* O 
4. 0 
3.0 
475 
>172 
IO 
IO 
do 
3.0 
3- O 
C. O 
3. 0 
C. O 
3. 0 
3. 7 
.do. 
0 w 
3.0 
0 w 
A . O 
j w 
A m O 
c. 0 
j w 
3* O 
3» O 
3* 7 
4*6 
660 
AO 
.do. 
e. O 
II. O 
Q. O 
9.0 
O w 
4* 0 
O w 
IO- 0 
8.0 
7.0 
7*9 
167 
60 
.do 
t, O 
ft, O 
7 w 
A- O 
3.0 
7- 0 
2- O 
5* 0 
±yj i 
600 
33 
.do. 
j* w 
7* ° 
7 w 
I* O 
3. O 
2* 0 
4.0 
43 
100 
Wheat. 
6.0 
2* O 
1-0 
3-o 
1-0 
1.0 
1.0 
• 0 
• 2 
. 2 
. 2 
1.0 
1*4 
128 
AO 
.do. 
• 2 
. c 
• 2 
• 2 
• 2 
• 2 
. 3 
108 
18 
.do. 
• 0 
• 3 
• 2 
* 2 
. 2 
400 
40 
.do. 
• 2 
• 2 
• 2 
• 2 
. 2 
42 
60 
.do. 
x.o 
2.0 
x.o 
2*0 
3-o 
2.0 
•5 
• 2 
. 2 
•5 
.j 
1.2 
• 1.0 
4.7 
75 
.do. 
• 2 
. 5 
• 2 
• 2 
• 2 
. 3 
4/ 
123 
50 
.do. 
2- O 
i- 0 
• 2 
♦ 2 
1.0 
.. i 
.9 
674. 
60 
..... do. 
2. O 
1.0 
3. 0 
4. 0 
3* 0 
2* O 
3* 0 
I. O 
2.4 
aq 6 
80 
.do. 
2* O 
2. 0 
I. O 
I* O 
3. 0 
I. O 
i* 7 
127 
90 
Oats. 
*5 
• 2 
♦ 5 
•5 
2* O 
5*o 
4.0 
2.0 
5-o 
4.0 
4-o 
2.0 
2*5 
I 
125 
20 
.do. 
• 2 
• 2 
- 0 
• 2 
• 2 
. 1 
. 2 
1 
IOO 
60 
... .do 
. 5 
• 2 
2- O 
• 2 
I- O 
. 5 
... j 
. 7 
f 1,7 
607 
35 
.do. 
3* 0 
3* 0 
A- O 
A- O 
3. 0 
3* 0 
i 
.i 
3.3 
J 
400 
40 
Timothy... 
. 2 
. 2 
*T V 
• 2 
1 
1 
j 
• 2 
. 2 
While the wheat-scab infection during this season was generally light, 
there was enough to show a striking difference in the percentage of scab 
resulting where wheat followed com and where wheat followed some 
other crop. In every field which had produced a corn crop during the pre¬ 
vious year the percentage of wheat scab was much higher than where 
some other crop had preceded wheat, the average of scab infection being 
more than 170 per cent higher than in any other crop sequence. 
The seasonal difference in the percentage of scab was due undoubtedly to 
weather conditions during the flowering and maturing of the wheat crop. 
It has been previously observed by Schmitz ( 18 ), Mortensen ( 16), Beck¬ 
with (2), Schaffnit (17), and others, that there is a greater abundance of 
wheat scab during moist seasons. Indications are that moisture was the 
chief factor in producing the seasonal differences in infection during these 
two years, as the weather during and following flowering in 1919 was very 
moist, whereas in 1920 the entire period was dry. Schaffnit (27), work¬ 
ing with Fusarium organisms isolated from scabbed cereals, has shown 
that a relative humidity of not less than 55 to 60 per cent is necessary 
for their growth and that the substratum must contain 20 to 30 per cent 
of moisture. 
STUDIES IN 1921 
In 1921, an effort was made to secure data under even more uniform 
conditions than in the previous years. After considerable scouting, four 
