96 SHADE TREES. 



WALNUT. Marsonia juglandis Lib. causes a brown spot 

 on the black walnut and butternut, gradually increasing in 

 size and frequently covering the entire leaflet. 



CHESTNUT. Marsonia ochroleuca B. and C. causes nu- 

 merous circular, ashy white spots on the chestnut. (Fig. 

 36.) The dead tissue of these spots breaks leaving holes 

 and the entire leaf finally turns brown and falls prematurely. 



ELM. Dothidea idmi Duv. attacks elms causing con- 

 spicuous black spots. Frequently the foliage is badly in- 

 fected and the beauty of the tree seriously marred. 



MAPLES. Rhyiisma acerium Pers. attacks many of the 

 maples, but is most severe on the silver maple, causing shiny, 

 black, hard, slightly elevated patches commonly known as 

 tar spots. (See below.) 



HORSE CHESTNUT. Phyllostida pavice Desm. is the cause 

 of an important leaf spot or blotch. The spots are irregular 

 in shape, increase rapidly in size until the greater part of 

 the leaf is brown and has the appearance of being sun-burned. 

 The leaves fall early and the vitality of the tree is reduced. 

 This fungus is frequently accompanied by others which aid 

 in its injurious work. 



CATALPA. P. catalpce Ell. and Mart, and Cercospora 

 catalpa? Wint. are the causes of unsightly leaf spots on the 

 catalpa. They are frequently accompanied by Macrosporium 

 catalpce E. and M. and Microsphcera elevata Burr. 



MAPLE. P. acericola C. and E. is the cause of a leaf spot 

 of the maple, which is frequently so severe as to cause a pre- 

 mature dropping of the foliage. (See above.) 



Treatment. 



The burning of the fallen leaves, thus destroying enormous 

 numbers of spores which could otherwise be distributed by 

 wind and water, will greatly reduce these diseases. Where 

 practical to do so, spraying with Bordeaux mixture will hold 

 them in check. 



