606 
Journal o f Agricultural Research 
Vol. XXX, No. 7 
British Columbia. The probability 
of overwintering of Cronartium ribicola 
does not seem to be greater in the 
Northwest than in the Northeastern 
States. 
It is not easy to predict accurately 
how rapidly the rust will move south¬ 
ward either west of the Cascades or 
in the “Inland Empire .” Its history 
indicates that its spread upon pine to 
the south is relatively slow, not over 
40 miles since it was introduced into 
Vancouver in 1910. The fact that 
north winds accompany dry seasons 
seems to be an important factor favor¬ 
ing a slower spread of the rust toward 
the south. On the other hand, Ribes 
nigrum, and to some extent other 
species of Ribes, may become infected 
in dry seasons like 1922, and a little 
pine infection may occur. The volume 
of aeciospore production is increasing 
each year in British Columbia. Infec¬ 
tion has appeared in the Puget Sound 
region for at least three.years in succes¬ 
sion. It is practically certain, therefore, 
that the rust will become established in 
western Washington within a few years. 
When it is once established there, and 
aeciospores are produced in considerable 
quantities, it will tend to spread into 
and through the Cascades to the north 
and east. Aeciospores may then be 
carried southward into Oregon and 
when it becomes established there 
north winds may carry aeciospores into 
southern Oregon and northern Cali¬ 
fornia. 
Although it is scarcely possible that 
much, if any, infection may occur in 
the sugar pine region (fig. 1) during the 
usual dry season, it is very probable 
that abundant infection may occur in 
the occasional wet summers such as 
those of 1888, 1906, and 1913. This 
possibility is emphasized by the presence 
of a similar rust, Cronartium pyriforme , 
upon the yellow pine in northern Cali¬ 
fornia. 
The white pine in the “Inland Em- 
pre” is in line with the prevailing winds 
from the coast. It is also in line with 
local currents which move southward 
along the Columbia and Kootenay 
Valleys. The spread of infection in 
1923 to Ribes nigrum in the interior of 
British Columbia and northeastern 
Washington shows that spores of the 
rust are practically certain to be car¬ 
ried into the white pine regions of 
Idaho and Montana. When this hap¬ 
pens, infection of pine will depend upon 
moisture conditions and the presence 
of susceptible Ribes. 
Comparison of the summer precipi¬ 
tation at various stations (Tables XII, 
XIII, and XIV) in the white pine 
districts shows less summer rainfall 
in the interior of British Columbia 
than upon the coast. It also shows 
less for Idaho and Montana than for 
places farther north in British Colum¬ 
bia. The average summer precipi¬ 
tation for these three districts is as 
follows. 13 Inches 
Coast region of British Columbia_ 6.58 
Interior of British Columbia_ 5.93 
Idaho and Montana_ 4.68 
These figures indicate, other condi¬ 
tions being equal, that infection of pine 
should be less severe in the interior than 
upon the coast of British Columbia. 
The relatively small amount of infec¬ 
tion thus far discovered in eastern 
British Columbia seems to substantiate 
this claim (see Table VIII). For the 
same reason infection should become 
established more slowly and be less 
severe in Idaho and Montana than in 
eastern British Columbia. 
The destruction of all infected pine 
material which has been found in 
eastern British Columbia should tend 
to retard the spread of the rust. 
It is a significant fact that all the 
pine infection in eastern British Co¬ 
lumbia can be attributed to Ribes 
nigrum and that practically all the 
infected Ribes found in the dry belt 
or east of it were this species. 
Climatic factors can not be changed 
materially by man, but the elimina¬ 
tion of Ribes nigrum from the pine 
districts of Idaho and Montana should 
lengthen greatly the time before the 
rust becomes established in these 
States. 
SUMMARY 
The white-pine blister rust has been 
in British Columbia at least since 1910. 
It became widespread by 1913. 
It has spread upon the white pine 
practically to the north and east limits 
of the coast belt of white pine. 
It has spread a relatively short dis¬ 
tance to the south. 
It has become established at four 
places in the eastern belt of white pine 
in British Columbia. 
An average of one season in every 
four years has been favorable for 
general spread of the disease along the 
coast of British Columbia. 
In the summer of 1922 there was 
infection of Ribes by aeciospores as 
far south as Ilwaco, Wash. In 1923 
infection was not found south of the 
vicinity of Port Townsend, Wash. 
18 These figures were obtained by taking an average for the six stations in each district with the greatest 
summer precipitation. The data for British Columbia is from “Climate of British Columbia,” by F. 
Napier Denison (3). 
