162 



AMERICAN FORESTRY 



the nursery. The tender young leaves and shoots are 

 attacked, causing them to turn black and to wither very 

 much, as in the case of severe attacks of plant lice or 

 conditions caused by long, severe droughts. The cherry 

 leaf spot differs from the others, in that it exists as a 

 circular hole in the leaf rather than as an area of dis- 

 colored tissue. For this reason it is known as the "shot- 

 hole" fungus. The wild cherry is the one most fre- 

 quently attacked. 



Over large areas there is no practical method of con- 

 trolling leaf spots. With highly valuable park or street 

 trees the trouble may be controlled in one of the follow- 

 ing manners : 



KUNGUS OX LOCUST TREKS 



Collect and burn the leaves of all infected trees. 



Spray the trees at the beginning of the growing season, 

 when the buds are unfolding, and again in July, using a 

 standard fungicidal spray. Lime-sulphur would be effec- 

 tive and safer to use than Bordeaux mixture, which 

 sometimes burns the foliage. 



FUNGUS DISEASES ATT.\CKING THE STEM AND BRANCHES 

 OF TREES 



This class of fungi may be roughly grouped into the 

 three classes which have been given above in this article. 

 Of these, the rusts are perhaps the most interesting. The 



peculiar interest of the class lies in the fact that most 

 species do not complete their life cycle on a single host 

 plant, but require two distinct plants. A few of the 

 most important and interesting of the class are : 



1. The Cedar Apple, attacking our common red cedar 

 and trees such as the apple, hawthorne, and shad-bush. 

 This disease frequently gives apple growers great con- 

 cern, as it causes much loss from "scabby" or otherwise 

 imperfect fruit. 



A WELL-KNOWN SPECIES 



These produce a decay which, in most instances, necessitates tree 

 repair. The directions for overcoming them should be carefully 

 read. 



2. The White Pine Blister Rust, attacking the stems 

 of white pine and the common garden currant or other 

 members of the genus ribes. 



3. The Fir Rust, attacking the leaves and twigs of the 

 balsam fir and other plants not yet discovered. This 

 disease causes the familiar Witches Broom of the fir. 



4. The Spruce Rust, attacking Norway spruce and the 

 leaves of the rhododendron and mountain laurel. 



CONTROL OF RUSTS 



These diseases may be controlled by the removal of 

 one of the host plants or by the application of fungicidal 

 sprays at the proper season. The first method is a rather 

 heroic one and is , therefore usually supplanted by the 

 second. Spraying for rusts will vary slightly with the 



