20 DISEASES OF DECIDUOUS FOREST TREES. 



considerable damage in osier willow plantations (93). Where the 

 disease is destructive the affected leaves which have fallen to the 

 ground should be raked together and burned. 



SYCAMORE LEAP-BLIGHT. 



The different species of sycamore, and more especially the common 

 sycamore (Platanus occidentalis L.), are very generally affected 

 throughout this country and Europe by a leaf and twig blight caused 

 by the fungus Gloeosporium nervisequum Sacc., which in its perfect 

 form is known as Gnomonia veneta (Sacc. & Speg.) Kleb. (45). This 

 fungus attacks the young leaves at about the time they reach full 

 growth. The attack usually takes place at or near a large vein of 

 the leaf, resulting in the stoppage of the water supply of considerable 

 areas of the leaf, thus leading to the death of these areas. The 

 deadened portions are usually located, as above indicated, along 

 the main veins of the leaf. Sometimes the attack is made on the 

 petiole of the leaf or on the young twig, causing the death of an 

 entire leaf or bunch of leaves. In severe attacks the leaves are 

 dropped prematurely, and if the attacks are continued with inten- 

 sity for several years the trees become seriously weakened, and may 

 even die outright. 



This trouble is exceedingly common of late years and occurs so 

 universally upon the sycamore that the damage is becoming notice- 

 able, especially upon the park and street trees. Raking together 

 the fallen leaves and burning them, pruning out dead twigs and 

 branches, and spraying with Bordeaux mixture where expense is 

 not a consideration should completely control this trouble (24, 35, 

 102). 



LEAF-SPOTS. 



A large number of minute forms of the imperfect fungi belonging 

 to the genera Cercospora, Phyllosticta, Ramularia, and Septoria 

 attack the foliage of many of the deciduous trees and cause the 

 so-called ''leaf -spots." Leaves affected with these diseases usually 

 exhibit more or less numerous deadened areas of small size. Early 

 in the season these spots are apparently sterile, but later a close 

 examination will reveal a number of tiny black specks located near 

 the middle of the area. These are the fruiting bodies of the fungus, 

 in which are produced the spores for the production of still other 

 colonies. The maple leaf -spot fungus (PJti/Uosticta acericola Cook 

 & Ellis) (24, 102) may be taken as a type of this class of diseases. 

 It is quite common upon the various species of maple, and in severe 

 attacks where a large proportion of the leaf surface is affected the 

 leaves drop prematurely. As a general thing, however, these dis- 



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