82 BULLETIN 957, U. S. DEPARTMENT OF AGRICULTURE. 
shipment of 5-leaved pines and of Ribes nigrum from the States 
of New England to any of the other States and from New York to 
points outside that State. Still more recently, an absolute embargo 
has been placed on ornamental and forest tree and shrub stock from 
other countries (fig. 13). 
These quarantines prevent our getting more of the white-pine 
blister rust from other countries. The Great Plains region forms a 
natural barrier (fig. 13) against the spread of this disease from the 
East to the West (97, 98, 141, p. 7; 148)). Since it is already well 
distributed and established east of this barrier, the immensely 
valuable western white pines can be protected very efficiently by 
preventing the shipment of white pines and Eibes from the infected 
section to the western region, which is still free from the disease. 
This is accomplished by quarantine, which is designed to prevent the 
shipment of infected stock from a generally infected district to those 
States which are not generally infected and to exclude plant pests 
from all the rest of the world (98). 
Within the past four years many of the various States have 
enforced regulatory measures with reference to this disease (94). 
These States are California, Delaware, Georgia, Idaho, Illinois, Indi- 
ana, Kansas, Maine, Maryland, Massachusetts, Michigan, Minnesota, 
Montana, Nevada. New Hampshire, New Jersey, New York, North 
Carolina, Oregon, Pennsylvania, Rhode Island, South Carolina, 
South Dakota, Tennessee, Vermont. Washington, West Virginia, 
and Wisconsin. 
ERADICATION OF ADVANCE INFECTIONS. 
In 1909, when Cronartium ribicola was first found upon white pines 
in North America, it appeared to occur only on recent shipments of 
young trees from Europe. That is, it was present in advance infec- 
tions, and so far as could be determined there was no generally 
infected area. Since that time areas have been found which are 
generally infected, and we have both types of infections to reckon 
with. (See figs. 2 to 12.) Where advance infections were small it 
appeared to be feasible to attempt eradication of the disease, but 
when generally infected areas were found eradication became impos- 
sible, and local control was the only feasible thing to be attempted. 
When this disease was first discovered on Ribes in 1906 at the 
Agricultural Experiment Station at Geneva, N. Y., an attempt was 
very properly made to eradicate the disease. All of the Ribes in the 
infected plat were destroyed. Very few white pines were within 
half a mile, and none of these were found diseased. Stewart (150) 
published an excellent account of this case. It was not then known 
that the seciospores readily blow for miles in a viable condition, nor 
was that fact established until rather recently (128, 145, 146). 
