and gooseberries, both wild and cultivated, from within and 

 about the areas to be regenerated to a distance of about three 

 hundred yards, under ordinary conditions. All of these 

 species, generally known as "Ribes," must be kept out of all 

 areas growing White Pine. 



Fortunately this work of eradicating wild currant and 

 gooseberry bushes is practical and provides an effective 

 method for the control of this disease. In fact, experimental 

 work already done by the Bureau of Plant Industry in co- 

 operation with the several States, shows conclusively that 

 eradication is not only economically possible, but produces 

 positive results in stopping the progress of the disease, as 

 shown in sample plots at Kittery Point and at Alfred, Maine. 

 In both cases eradication was done in 1917, and no new 

 infections have been found since that date on either of these 

 areas. 



Blister Rust enters the tree through the leaves or 

 needles, and the disease works slowly down through the leaf 

 tissues and the cambium, the fruiting stage occurring as 

 long as four years after the original infection has taken 

 place. 



It is a parasitic plant which lives in its alternate stages 

 in the inner bark of white pine trees and in the leaves of all 

 known kinds of currant and gooseberry bushes. It is but 

 one of a large number of parasitic fungi or rusts, such as the 

 Wheat Rust, which has its alternate stage on the barberry, 

 and the Apple Rust which has its alternate stage on Cedar. 

 Without the two different plant hosts to live on, they can not 

 complete their life cycle and therefore they die without 

 spreading. It can not go directly from one pine tree to 

 another, without the intermediate stage on some species of 

 Ribes. 



The rust is most easily distinguished on pine from the 

 middle of April to the middle of June, when it shows up as 

 orange-yellow blisters on the bark of the pine. These blis- 

 ters are filled with fine dust-like spores, which are carried by 

 the wind to great distances, where they germinate on the 

 under surface of the leaves of either currant or gooseberry 

 bushes. The diseased areas in the bark are surrounded by 

 a discoloration of a yellowish or bronze tinge, and later in 

 the season the injured bark cracks up in irregular fissures 

 and plates. 



The leaves of the currant and gooseberry again produce 

 bright orange-yellow spores about ten days after infection, 

 on the under side of the leaves. This constitutes the early 

 summer stage of the disease on Ribes, and the spores pro- 



76 



