Oct. 30,1916 Spongospora subterranea and Phoma tuberosa 
229 
about 50 inspectors. By that time 12 per cent of the crop had been dug 
and much of it doubtless thereby saved from infection. Were infection 
to appear as late* every season, early harvesting would be a very simple 
and effective means of avoiding the disease. 
The results obtained in 1914 suggested early harvesting as a means of 
wholly avoiding the disease where the crop was growing on land known to 
be infected. To test this four rows 16 rods long were planted on infected 
land in 1915. Two of these rows were harvested on August 15, when 
about two-thirds mature, or about two weeks earlier than usual, the har¬ 
vesting season here beginning about September 1 and extending to Octo¬ 
ber 10. The remaining two rows were dug on October 10. The two rows 
dug in August produced 323 pounds; of this lot 153 tubers were infected. 
The two dug in October produced 412 pounds, of which 167 tubers were 
infected. These figures show that practically all the infection in 1915 
made its appearance before August 15, and that from the standpoint of 
control nothing was gained by harvesting on August 15, while 89 pounds 
of potatoes were lost in the two rows harvested at that time. However, 
had infection taken place as late in 1915 as it did in 1914, the crop on a 
given farm might have been harvested before it became infected; conse¬ 
quently it is believed that this line of attack has not been exhausted and 
that it has greater possibilities than the results obtained in 1915 indicate. 
SEED TREATMENT 
In the spring of 1914 an experiment to control the disease by disin¬ 
fecting the seed potatoes badly infected with Spongospora subterranea 
was begun, Green Mountain, the variety commonly grown in northern 
Maine, being used. The seed was treated as shown in Table VI. 
Table VI .—Results of experiments in controlling powdery-scab by seed treatment in igi4 
Plot 
No. 
Treatment. 
Average 
weight. 
Total 
num¬ 
ber. 
Hills. 
Num¬ 
ber 
sound. 
Num¬ 
ber in¬ 
fected. 
Per¬ 
cent¬ 
age of 
infec¬ 
tion. 
Pounds. 
I : 
Check, infected seed. 
i -39 
200 
63 
137 
6S.0 
2 ; 
Seed wet and rolled in sulphur.. 
1.48 
152 
85 
67 
44.0 
3 
Formaldehyde (1:30), hours... 
i- 27 
164 
138 
26 
15-8 
4 
Atomic sulphur <5 per cent), iM hours. 
i- IS 
202 
148 
54 
26. 7 
5 i 
Formaldehyde (2:30), hours. 
1. 04 
136 
116 
20 
14. 7 
6 
Mercuric chlorid (2:15), x% hours. 
1.05 
189 
184 
4 
2.0 
Check, infected seed... 
164 
92 
70 
42.0 
t 
8 
Copper sulphate (5 per cent), iJ 4 hours. 
•94 
142 
137 
5 
3 - 5 
9 
Mercuric chlorid (4:15), 53°-*54°C., 5minutes. 
•93 
75 
70 
5 
6.6 
10 
Formaldehyde (2:30), 46-50° C., 5 minutes. 
.90 
55 
54 
1 
1.8 
n 
Mercuric chlorid (4:15), 44°-45°C., 5 minutes. 
1.14 
75 
69 
6 
8.0 
12 
Check, healthy seed. 
1.25 
200 
198 
2 
1.0 
