18 
BULLETIN 1156, U. S. DEPARTMENT OF AGRICULTURE. 
The production of this wart-immune seed is Aery carefully regu- 
lated bv the Pennsylvania Department of Agriculture in order to be 
certain that each variety is free from mixtures. For the season of 
1921 approximately 10,000 bushels of Spaulding Rose potatoes were, 
grown in Potter County, Pa., and distributed to growers in the quar- 
antined areas through the ordinary commercial channels. The 
results of the first season of the general use of immune varieties have 
proved very successful, as the newly introduced immune varieties are 
far superior to the varieties formerly grown in general appearance, 
stand, and yield. 
As a further means of preventing the spread of potato wart, it was 
decided in 1921 to establish a safety zone, surrounding the quaran- 
tined area. (Fig. 3.) This area is largely agricultural, comprising 
2,000 farms' and a few 
scattered rural villages, 
and since it comprises 
and includes all the culti- 
vated land for several 
miles on every side of the 
wart-infested region the 
value of this zone in pre- 
venting the spread of 
the disease is obvious. 
Within this area after 
April 1, 1922, only wart- 
immune varieties could 
be grown. 
The varieties selected 
for the safety zone are 
Irish Cobbler and Green 
Mountain, the former an 
early and the latter a late 
variety. To furnish the 
large supply of seed pota- 
toes needed in 1922 the 
potato growers of the 
safety zone organized 
potato associations and brought in and grew during the season of 
1921 under State inspection and supervision 50,000 bushels of Green 
Mountain and Irish Cobbler potatoes. To obtain experimental data 
as to the adaptability of these varieties to the safety zone, these 
potatoes were grown on 42 different farms in the three portions of 
the counties comprising the safety zone, where they produced an 
average yield of 360 bushels per acre, as compared with an average 
of 225 bushels per acre for local varieties. 
The experience gained in connection with the supervision of the 
seed production of wart-immune varieties for the quarantined area 
has emphasized the absolute necessity of careful inspection and regu- 
lation. The loose application of a multitude of names to various 
strains of our commercial varieties has resulted in such uncertainty 
in regard to the identity of any individual stock that it has been 
found necessary to test every prospective seed stock for wart im- 
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Fig. 3.— Outline map of Luzerne and Carbon Counties and por- 
tions of Columbia and Schuylkill Counties, Pa., showing the 
area heavily infested by potato wait (marked by cross hatch- 
ing) which is under rigid quarantine and the surrounding 
safety zone (marked by small dots'! in which a limited quar- 
antine is maintained. 
