Apr. 1, 1925 
Relation of Weather to White Pine Blister Rust 
605 
from Beaton or Revelstoke. These 
places are all in the path of the pre¬ 
vailing winds from the coast. There 
are frequently strong surface winds 
which blow up through the valley 
along the Pacific Great Eastern Rail¬ 
way and over the divide into the 
interior. 
The widespread infection of black 
currants in 1923 at many places in the 
dry belt, as well as to the east of it, is 
further evidence of wind dissemination. 
A glance at the map shows that these 
places also are all east of the region 
of heavy pine infection and in line with 
the prevailing westerly winds from 
the coast. 
The widely distributed infection of 
Ribes in western Washington in the 
season of 1922 must have been caused 
by long-distance spread of aeciospores 
from British Columbia. This was 
made possible by the enormous number 
of spores produced through an un¬ 
usually long season, from the middle 
of May until the middle of July, and 
by the unusual amount of northerly 
winds at certain periods which came 
down the Strait of Georgia, through 
Puget Sound, and spread over the 
country to the south and west. 
All the evidence seems to indi¬ 
cate that long-distance spread of the 
rust has been caused by wind-borne 
aeciospores. The only remaining ex¬ 
planation requires long-distance spread 
by uredospores or a gradual spread 
and overwintering upon Ribes. Long¬ 
distance dissemination of uredospores 
would be much more remarkable than 
long distance dissemination of aecio¬ 
spores. All field studies made by the 
writer in the East as well as in the 
West fail to show any considerable 
spread of the rust by uredospores (6). 
Overwintering upon Ribes nigrum has 
been demonstrated twice under ex¬ 
perimental conditions. On the other 
hand, many experiments have given 
negative results. Field observations 
have never shown that the rust has 
overwintered upon either cultivated 
or wild Ribes ( 8 , p. 68-71). The rust 
did not survive the winter of 1922-23 
upon R. nigrum in the Willapa Bay 
region of southwestern Washington. 
The bushes on four plantations, all 
heavily infected in 1922, failed to show 
any infection in 1923. These were 
examined in June and again the last 
week in August. All the other R. 
nigrum in this part of the State were 
eradicated in 1922. The plants in 
question were to be destroyed in the 
autumn of 1923. 
It is very improbable that these 
spores came from local pine infections 
in Washington. The distribution of 
the infected Ribes indicated a distant 
source of spores. If the spores did not 
come a long distance there must have 
been many local centers of infection. 
Thorough scouting, however, failed to 
show any fruiting cankers in Washing¬ 
ton. Many of the infected Ribes, 
particularly those in the Willapa Bay 
region, were long distances from any 
five-needle pines. (See figs. 1 and 2.) 
Aeciospores are well adapted for 
dissemination by air currents. They 
are dry and powdery and retain their 
vitality for many days or weeks under 
adverse conditions. Smut spores are 
known to be carried long distances by 
wind ( 4 .) Spores of wheat rust have 
been found over 10,000 feet above the 
surface of the earth (9 ). 12 
All the species of Ribes found in 
British Columbia were in a dormant 
condition and without leaves by the 
middle of December, 1922, and they 
so remained until April, 1923. In 
February, 1923, many plantations of 
Ribes nigrum were examined in Wash¬ 
ington and in Oregon as far south as 
Ashland. All were found to be perfectly 
dormant, without leaves and with no 
buds opening. Below Roseburg, Oreg., 
some wild Ribes were found with a few 
green leaves of 1922, and buds begin¬ 
ning to open. All the Ribes seen in 
Washington were in a dormant condi¬ 
tion at that time. It has been re¬ 
ported, however, that R. sanguinium 
as far north as Seattle holds a few of 
its old leaves until the next season’s 
buds open. It appears that the 
chances for overwintering were very 
slight even if there had been uredo¬ 
spores upon the old leaves. Many 
infected R. nigrum leaves collected late 
in October and in November, 1922, 
were examined. No uredospores, how¬ 
ever, could be found upon them. 
In the vicinity of Port Townsend, 
infection was found again in 1923 
upon Ribes in the same locality in 
which it appeared in 1922. In one 
instance the same plants of R. brae - 
teosum and R. divaricatum were found 
with infection in 1922 and in 1923. 
These were some 9 or 10 miles from the 
R. nigrum which were found infected 
in 1921. This place is near Puget 
Sound, less than 80 miles from infected 
pine in British Columbia. It is alto¬ 
gether probable that these plants as 
well as many others in favorable situa¬ 
tions upon Puget Sound may become 
infected each year by aeciospores from 
12 Since this paper was submitted for publication, J. A. Larsen (5) has called attention to wind dissemina¬ 
tion of dust from Oregon and Washington to northern Idaho and Montana. 
