June 21, 1924 
Survey of Blister Bust Infection of Pines 
1255 
The predominant effect of the patch of cultivated black currants in causing 
infection as compared to the possible effect of the other Ribes found on the area 
is shown in figure 2. The percentage of infected trees in concentric 100-foot 
zones from the black currants shows pronounced and fairly regular decreases in 
the four directions of the compass, whereas this would not be the case in simi¬ 
larly spaced zones circumscribing any other point as an infection center. The 
highest percentages of infection, when considered in relation to the location of 
the black currants, are in the paths of the late summer and autumn storm winds. 
On this basis, infection emanating from the patch of black currants was traceable 
in diminishing degrees for distances of 600 to 900 feet while infection from other 
Ribes was comparatively meager on nearby pines and not traceable beyond 200 
feet. 
RATE OF INFECTION OF STAND 
The blister rust became measurably established on pines in the west half of 
the area studied at Kittery Point in 1901. From 1901 to 1916, inclusive, 34.5 
per cent of the trees became infected. The rate at which the stand became in¬ 
fected increased from a yearly average of 0.225 per cent during the first 4-year 
period to a yearly average of 4.6 per cent during the last 4-year period preceding 
the eradication of Ribes. 
Table I.— Rate of infection of stand a 
First 
4-year 
period 
(1901-1904) 
Second 
4-year 
period 
(1905-1908) 
Third 
4-year 
period 
(1909-1912) 
Fourth 
4-year 
period 
(1913-1916) 
Total number of healthy trees at beginning of 4-year 
period... 
6,727 
6,666 
6,317 
5,386 
Number healthy trees that became infected during the 
4-year period........— 
61 
349 
931 
986 
Per cent of healthy trees that became infected during 
4-year period_____ 
0.9 
5.2 
14.7 
18.3 
a Table I is compiled from the data on the west half of the experimental area shown in Figure 1. 
SEVERITY OF INFECTION ON PINES OF DIFFERENT SIZE CLASSES 
The percentage of infection was lowest among trees of the smallest size and 
highest among trees of the largest size. Table II indicates that on the area 
studied the percentages of trees infected are correlative to their diameter-size 
classes. 
Table II.— Percentage of pines infected, by diameter classes a 
Diameter breast 
high 
Number 
of pines 
Trees 
infected 
Inches 
1 and under. 
3,752 
700 
Per cent 
21 
2 ... 
43 ) 37 * 3 
3. 
412 
4___ 
338 
«) 42 - 3 
5.... 
264 
6 ... 
165 
81)87.5 
7.... 
160 
8 .... 
169 
62\«n e 
9___. 
155 
59 / 60 ' 5 
10.. 
149 
71 W 8 
60/ 00 '® 
11... 
130 
12... 
109 
66)74 7 
79J 74 ‘ 7 
13 and over.___ 
224 
a Table II is compiled from the data on the west half of the experimental area shown in Figure 1. 
