WHITE-PTXE BLrSTER 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 seciospores 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 Cwnartium 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 bj^ 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 strohus is 

 rapidly developing. A strip survey in one locahty 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 o\\Tiers 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. 



