Ornamental and Shade Trees 



A Department for the Advice and Instruction of Members of the American Forestry Association. 



Edited by J. J. Levison, B. A., M. F. 



FUNGUS DISEASES OF TREES 



By R. B. Maxwell 

 City Forester, Baltimore, Maryland 



THE fungus diseases of trees are produced by the 

 action of plants. These plants differ from those 

 seen about us, in that they contain no chlorophyll, 

 or the green coloring matter which is common with the 

 "green" or higher plants, and they derive their nutriment 

 directly from the trees rather than from the soil. A 

 fungus disease which derives its food from a living plant 

 is a parasite, while one deriving its sustenance from a 

 dead plant is called a saprophyte. Since arboriculture 

 deals only with living trees, arborists are not interested in 

 saprophytes. Parasitic fungi, as a rule, gain entrance to a 

 tree through wounds caused from abrasion, shock, or im- 

 proper pruning. After having become established, the 

 fungus begins to develop small rootlets, called myceleum, 

 which are pushed out into the tree tissues as a means 

 of anchoring the disease plant and of obtaining food. 

 As a result of the action of certain little-understood 

 stimuli upon the myceleum, a substance is secreted which 

 results in decay or the breaking down of the tree tissues. 

 This, then, is the process which has resulted in unsightly 

 cavities, diseased areas, and frequently discolored or 

 distorted foliage. 



In considering this question, let us study it in a broad 

 and general manner, from the viewpoint of those charged 

 with the care of trees. We shall attempt to identify the 

 diseases from the form and character of their fruiting 

 bodies and from the nature of attack, endeavoring to 

 apply curative measures, or to so conduct our cultural 

 operations as to prevent the occurrence of such troubles. 



For the sake of convenience, let us divide the tree 

 diseases into three rough groups : 



1. Fungus diseases attacking the leaves of trees. 



2. Fungus diseases attacking the stem and branches of 

 trees. 



fa) The rusts. 



(b) Those with inconspicuous or hidden fruiting 

 bodies. 



(c) Those with conspicuous fruiting bodies. 



'!. Fungus diseases attacking the roots of trees. 



FUNGUS DISEASES ATTACKING THE LEAVES OF TREES 



These diseases are for the most part not dangerous, 

 but are worthy of consideration, since their action is fre- 

 quently responsible for the marred beauty of our fine 

 specimen trees. The troubles are known as "leaf spots," 

 and belong to the general class of fungi known as molds 



and slime molds. The following trees are frequently 

 attacked by the leaf -spot troubles: American chestnut, 

 Norway and red maples, American and European lindens, 

 black walnut, American sycamore, black oaks, catalpa, 

 horse-chestnut, aspens, wild cherry, and magnolia. Of 

 the above leaf spots that of the sycamore tree, the Nor- 

 way maple, and the horse-chestnut are usually the most 

 serious. The American sycamore is sometimes entirely 

 defoliated by its leaf spot. The leaf trouble of the Nor- 

 way maple is usually most serious with young trees in 



TWO SPECIES OF POMES 

 These are found nn a larpe number of deciduous trees and a few 

 evergreens. Members of this group attack beech, maple, yellow 

 birch, sycamore, asli, and black locust. 



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