BUREAU OF ENTOMOLOGY AND PLANT QUARANTINE 41 
SPREAD OF BLISTER RUST IN 1938 
Information on the spread of the disease is used in planning con- 
trol work. Ribes eradication is carried out around local pine stands 
of sufficient value to justif} 7 the expense of protection, and such pro- 
tection is effective regardless of the amount of disease in the vicinity. 
Blister rust control work, accordingly, is not primarily directed at 
retarding the spread of infection to new localities but is carried out, 
where practicable, to prevent injury to valuable pine stands before 
the disease arrives in a locality, as well as after it has become estab- 
lished in forest areas. 
During the calendar year 1938 blister rust was found for the first 
time on either white pine or Ribes in 70 counties. Six of these coun- 
ties are in the southern Appalachian States, 60 in the North Central 
States, 2 in Montana, and 2 in California. 
In the southern Appalachian States the rust was found on white 
pine in Highland County. Va.. and on Ribes in four counties in Vir- 
ginia and one in West Virginia. These discoveries did not extend 
the spread of the disease farther south but added new counties within 
the previously known limits of infection in the southern Appalachian 
region. 
The most extensive spread into new territory occurred in the North 
Central States, where weather conditions appeared to be more favor- 
able for the dissemination of the rust. Infection was found for the 
first time on white pine in 8 counties in Ohio, Michigan, and Wis- 
consin and on Ribes in 55 counties in Ohio, Michigan, Wisconsin, 
Minnesota. Indiana, Illinois, and Iowa. In 38 of the 55 counties in- 
fection occurred on the cultivated black currant (Ribes nigrum). 
The large number of counties in which the disease was found on 
cultivated black currants indicates the importance of this species as 
a disseminator of the rust and the need for the eradication of these 
plants in regions where white pines are valuable forest and orna- 
mental trees. The southern limits of the known infected area have 
been extended during the year from 1 to 3 counties in Ohio, Indiana, 
Illinois, and Iowa. In addition, many newly infected counties were 
added within the previously known limits of spread. 
In Montana the disease was found widely distributed on wild 
Ribes on both sides of the Continental Divide. Infection was found 
at five different points where inspections were made in Glacier Na- 
tional Park. This represents an eastward extension of the rust into 
Flathead and Glacier Counties. Glacier National Park is situated 
within these counties. 
During 1938 rust infection was found on Ribes in California 35 
miles farther south than before and is now present about 160 miles 
below the Oregon-California border. Numerous other infections on 
Ribes were found within the sugar pine area previously reported as 
infected No rust was found on sugar pine south of the vicinity of 
the Oregon-California border, but since it takes from 3 to 4 years 
after infection for the resulting cankers to become easily discernible 
on pines, sufficient time has not elapsed since discovery of the disease 
in the State to enable the field men to find it readily on sugar pine. 
However, it is very probable that scattered pine infections exist in 
several sections of northern California. 
