544 
Journal of Agricultural Research 
voi. xxxi. No. e 
Table III. — The effect of the previous crop — Continued 
B—As Indicated in All Fields Considered in Northern Maine 
1919 
1921 
Previous crop 
Number 
of 
varieties 
Number 
of 
fields 
Acreage 
Per cent 
infested 
Number 
of 
varieties 
Number 
of 
fields 
Acreage 
Per cent 
infested 
Potatoes. . 
4 
26 
259 
56.07 
3 
11 
61 
95.45 
Sod_ 
7 
31 
427 
24.51 
4 
16 
212 
73.81 
C—As Indicated in All Fields Considered in Western New York 
Previous crop 
Number 
of 
varieties 
Number 
of 
fields 
Acreage 
Per cent 
infested 
Potatoes..__ _ _ ___ 
4 
5 
46.75 
76.2 
Sod_ _ __ __ 
6 
23 
179.4 
32.8 
Under western New York conditions the same relation holds true 
(Part C, Table III). 
EARLINESS 
A third variable factor influencing the percentage of infestation is 
the earliness with which the plants make their appearance above 
ground. This is usually thought of in terms of planting date, or 
variety, or fertility of the soil, but in any case the result is the same. 
If a field is planted to an early variety such as Irish Cobbler, or if a 
late variety is planted early or in a favorable situation where it 
receives a stimulus to earlv and rapid growth, the percentage of 
infestation will be very much greater. The potatoes which come up 
earliest are infested first, and natural dispersal to varieties appearing 
later is slow and usually inconsiderable except where influenced by 
spraying. An indication of how this factor operates in adjacent 
fields in which all factors remain the same except the earliness with 
which the plants push through the top soil is shown in Table IV. 
Table IV. — The influence of variety 
Typical Adjoining Fields of Same Variety Planted Early and Late 
Field 
No. 
Variety 
Acreage 
Fertilizer 
Ridging 
Previous crop 
Planted 
Per cent 
infested 
1927 
/SpanMmfr 
\Rose__ 
30 
4-8-6 
High__ _ 
Sod__ 
May 5 
40 
1933 
{.Rose—'_ -- 
5 
4-8-2 
Medium_ 
Sod--. 
May 20 
20 
1928 
/Bliss 
20 
4-8-6 
High___ 
Sod-. 
June 10 
14 
\Trinmph 
1930 
Trish Hobhler 
30 
4-8-6 
High_ 
Sod__ 
May 10 
65 
Colorado potato beetles do not select early varieties exclusively, 
neither do they shift from late to early variety habitually. A late 
variety planted early will “trap-crop” for early varieties planted 
late, as may be noted by comparing the results in the adjoining 
fields Nos. 1927, 1928, and 1930. 
