BOARD OF HORTICULTURE 177 



England, New York and the Lake states. The damage which it annually causes 

 to those forest« is rapidly increasing, although it has not as yet become the 

 menace that it is in Europe. 



The White Pine Blister Rust 



Tliis disease is not an insect, as many erroneously suppose, but a plant disease 

 which attacks all five-leaf pines. Fortunately this is a disease which like the 

 wheat rust requires another host plant in order to complete its entire life. This 

 host plant is some species of wild or cultivated currants and gooseberries 

 (Ribes and Grossularia). (See Fig. 1.) This disease is one which affects the bark 

 of the pine, producing large cankers which eventually kill young growth and maim 

 and disfigure old trees by shiitting off the supply of sap. In time there appear 

 along the swelling of these cankers numerous white blisters, which eventually 

 break opeu, disseminating orange-colored spores of a powdery nature. (See 

 Fig. 2.) These may be noticed from April to the middle of June, and often later. 

 The spores are blown far and wide by the wind, or carried by birds and insects. 

 These spores can not reinfect pine, but should they happen to reach currants or 

 gooseberries, the other stage of the disease is started on the leaf appearing on the 

 underside as a rust. The spores produced on these leaves are also yellow or 

 orange in color, and may re-infect other currant and gooseberry bushes enabling 

 it to spread over a wide area. Later on there is produced another set of spores, 

 brownish in color, which can only infect the pines. (See Fig. 3.) Thus the 

 cycle is kept up indefinitely. The yellow, or summer stage, may be noticed on 

 the leaves of wild and cultivated currants and gooseberries from June 1 to the 

 fall of the leaves. The brown hair, or autumn stage (see Fig. 3) may be 

 noticed about August 1, often occuring on the same leaves which are still bearing 

 the summer stage. Specimens of the disease may be seen at the office of the 

 Secretary of the State Board of Horticulture in Portland. 



Special attention should be paid to the cultivated black currant, as this is 

 the most susceptible variety. Some recent evidence by government pathologists 

 Shows that the disease can winter over on currant and gooseberry plants as well 

 as on the white pines. 



Methods of Control in the East 



When the seriousness of this diseases in the United States was realized, state 

 and federal authorities endeavored to stamp it out. But it had spread so rapidly 

 over large areas that complete eradicalion was impractical. By completely eradi- 

 cating the currants and gooselierries in and near a white pine forest the disease 

 can be controlled. Due to the intensive forestry methods, and the fine Stands 

 of white pine in the eastern states, this method of control was found feasible. 

 No spraying of any sort has been found advantageous in even Controlling the 

 disease. 



The cost of control work on a quarter of a million acres in the New England 

 States in 1920 averaged only 2-1 cents per acre. In some other states the cost 

 exceeded $1.00 per acre but even much higher costs are insignificant compared to 

 the income producing value of eastern pine. On this basis the production of 

 white pine timber can l)e carried on profitably, in spite of the disease. But such 

 control measures would be manifestly impractical in the West. Here the white 

 pines occur over immense Stretches of rough mountainous country, and as a small 

 percentage of a mixed stand. Several species of wild currants and gooseberries 

 are present in great abundance throughout these regions. These conditions 

 would make it very difficult, if not impossible, to check the disease once it became 

 firmly established in the western white pine and sugar forests. 



White Pines in Oregon 



The immense Stands of white pine in the West are in danger of attack liy this 

 disease if ever the infection is carried this far. These Stands contain a supply 



