WHITE-PINE BLTSTER RUST. 89 
In a region where Ribes are rare or practically absent the removal 
of the diseased pines only may serve to prevent progress of the disease. 
This allows the dispersal of aeciospores and may result in scattering 
infection on Ribes miles away. In such cases it will take a long time 
to detect the escape of the fungus. In areas free from the Ribes the 
aim should be eradication rather than control of the disease, as such 
areas are the very ones where white pines should be grown in the 
future. 
In generally infected districts where Ribes are removed for some 
distance, it may pay to cut out the worst infected trees to reduce the 
crop of seciospores and thus reduce infection around the borders of 
the treated area. 
Status of the Control of White-Pine Blister Rust. 
The present status of the control of the white-pine blister rust in 
North America may be summed up as follows : 
Eradication of Cronartium ribicola is impossible except in small, isolated, advance 
infections. It should be attempted only in localities where the disease is quite lim- 
ited in distribution and well separated from the known generally infected areas shown 
in figure 2. As a national problem, control is the only feasible thing. Protection of 
uninfected or sparsely infected areas by enforcement of the present Federal quaran- 
tines is necessary, since this disease is distributed to great distances only by means of 
infected nursery stock. The western forests of white pines can be protected from the 
blister rust for an indefinite period by rigid enforcement of the Mississippi Valley 
quarantine. A single diseased shipment may undo all attempts to restrict it to the 
eastern forests. 
In the eastern forests blister-rust infection on Pinus strobus is 
rapidly developing. A strip survey in one locality in New Hampshire 
(24) shows that one-fourth of the white pines on an area of 72 square 
miles are now infected. The areas marked as generally infected in 
figure 2 show the great increase in general pine infection. Much of 
this infection will become visible in the next three years. It is an 
insidious disease, a tree not being noticed as diseased until it is 
heavily infected. There is abundant evidence that it is destructive 
to merchantable trees as well as to younger ones. It is just getting 
under headway. 
Ribes nigrum is far the most dangerous species, but all Ribes are 
dangerous to white pines in generally infected areas. In such areas 
the disease can be controlled by the removal of all Ribes. Local con- 
trol depends on the removal of Ribes within white-pine areas and 
the education of the white-pine owners to remove Ribes as a routine 
part of white-pine forest management. Local control by the removal 
of Ribes can be taken up at any time in the future, but if the present 
stand of trees is to be saved action must be taken at once. 
