82 BULLETIN" 957, U, S. DEPAETMENT OF AGRICULTURE. 



shipment of 5-leaved pines and of Rihes 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 efiiciently by 

 preventing the shipment of white pines and Ribes 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). 



