542 
Journal of Agricultural Research 
Vol. XXXI, No. 6 
absence of foliage injuries. The figure indicates, but does not repre¬ 
sent, the degree of severity of the infestation. Tabulation and com¬ 
parison of tnese readings indicate that the only variables affecting 
the percentage of infestation are earliness of appearance of the 
potato shoot above ground, type of ridge cultivation (covering 
operation), the nature of the previous crop, the application of the 
early sprays, and the proximity of wild or “ volunteer” potato plants. 
PROTECTION OF EARLY COVERING 
The “ridge” rather than the “hill” method of cultivation is 
followed consistently throughout the district in northern Maine from 
which figures were • obtained. After breaking up the soil with a 
4-inch cultivation, a disk hoe (occasionally a blade hoe) is used to 
throw the loose soil into a somewhat sharp ridge. Naturally, a 
deeper cultivation results in higher ridges. Ridging is begun when 
the potato sprouts first break through the surface soil. The sprouts 
are covered to a depth of 2 or more inches. The practice is then 
repeated as soon as the sprouts appear again, and sometimes they 
are covered for a third time before the rate of growth becomes too 
rapid to keep the sprouts covered. Ridge cultivation confers several 
advantages m addition to protecting the young plants from infesta¬ 
tion. Great variation occurs in the height as well as the care with 
which the ridge is constructed during the covering operation as 
well as subsequently. In this paper it is indicated whether a low, 
medium, or high ridging was practiced. In general, high-ridge cul¬ 
tivation is correlated with more compact covering. An indication 
of the protection afforded by the covering operation may be seen in 
Table I, which gives data taken from adjacent fields where, other 
conditions remaining the same, both low and high ridging were 
practiced side by side. 
Table I.— High-ridge versus low-ridge cultivation 
A.—In Typical and Adjoining Fields 
Field 
No. 
Variety 
Planted 
Fertilizer 
Previous crop 
Ridging 
Per cent 
infested 
136 
137 
Bliss TVinmnb 
May 21 
May 18 
4-8-4 
4-8-4 
Potatoes_ 
High. 
20 
100 
Li 
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Low_ 
B.—As Indicated in All Fields Studied 
Type of ridging 
1919 
1921 
Number 
of 
varieties 
Number 
of 
fields 
Acreage 
Per cent 
infested 
Number 
of 
varieties 
Number 
of 
fields 
Acreage 
Per cent 
infested 
Low ridging_ 
4 
7 
35. 
82.57 
3 
9 
60 
97.22 
Medium ridging- 
6 
27 
445 
36.66 
4 
10 
50 
84.70 
High ridging- 
6 
23 
206 
23.08 
3 
8 
186 
63.62 
t i ** * ’ « * ’ t ' * ' 
Ridging is not uniformly the practice in western New York, and 
where this method is followed it is not always done early enough 
to cover the shoots. Here growers cover more often for weed eradi- 
