Mar. 15 , 1924 
Wheat Scab , Corn Rootrot , and Crop Successions 867 
Table IV .—Percentages of stalk surface covered with perithecia of Gibberella saubinetii 
on old stalks of Yellow Dent corn in strains highly resistant, comparatively resistant, 
and susceptible to corn rootrot. Data obtained at Bloomington, III., in 1921 
1. 
2. 
3 - 
4 - 
5 - 
6 . 
7 - 
8 . 
9 - 
10 
11 
12 
13 
14, 
i 5 
16. 
17 
18. 
19 
20. 
21. 
Average 
Percentages of surface covered with Gib¬ 
berella perithecia. 
Stalk No. 
Most resist¬ 
ant selec¬ 
tion. 
Compara¬ 
tively resist¬ 
ant. 
Susceptible. 
6. 2 
3-7 
2. o 
o 
7 - S 
6.5 
4.4 
2. 2 
2. 8 
4.4 
i- 7 
4. 1 
o 
i -5 
2. 5 
S-o 
2. 8 
• 7 
i*7 
3-3 
4.3 
5*7 
3-5 
5-8 
4.4 
2.9 
7.0 
2.5 
15.0 
1. o 
3 - 9 
1 - 5 
4 - 5 
2. 2 
10.9 
2 - 5 
14. 5 
9 - 5 
19. 2 
6.7 
ii. 5 
5-0 
5-5 
4*4 
4.5 
13. 2 
11. o 
13 - 5 
10. 5 
6. o 
5-2 
5 - 7 
12. 2 
3-3 
4-3 
8.9 
SUMMARY OF THE THREE YEARS* DATA 
The three years* data as summarized in Table V, and presented graph¬ 
ically in Figure 1, give the average percentages of scab under three dif¬ 
ferent seasonal conditions, that is, a high amount of scab in 1919, a low 
amount in 1920, and a medium amount in 1921. These seasonal differ¬ 
ences are undoubtedly due to weather conditions and can not be con¬ 
trolled, but the relative abundance of scab each year, whether large or 
small, varies with the previous cropping, and is within the control of 
the farmer. Whether the average percentage of infection from season 
to season is large or small, the farmer who sows wheat after com can 
easily reduce the infection 50 per cent by using a different crop sequence 
in his rotations. 
Table V .—Average percentages of scab on wheat following various crops in seven States 
in 1919, and in McLean County , III., in 1920 and 1921, being a summary of Tables 
I, III, and IV 
Year. 
Average percentage of wheat-scab infection after previous crop of— 
Corn. 
Wheat. 
Rye. 
Oats. 
Clover. 
Timothy. 
! 9 I 9 . 
43-3 
4. 6 
17-4 
29. 2 
1. O 
3-7 
27. O 
22. 7 
1-7 
5.3 
II. 4 
8.3 
. 2 
JQ20 . 
TQ2T . 
