SHADE TREES. 



191 



Fig. 63. — Oyster mush- 

 room (Pleurotus 

 sapidus) on maple, 

 following injury. 



Maple (Acer). — Leaf spot {Phyllosticta acericolu C. & E.) forms irregular 



brownish spots on the leaves of the rock and white maples. 



Anthracnose (Glceosporium aqwcryptum E. & E.) is known to cause serious in- 

 jury to the leaves and shoots of the box elder and maple. 

 Leaf spot (Rhytisma acerinum Fr.) is characterized by 

 conspicuous black spots on the leaves of the red and white 

 maples, but is practically harmless. 



Ncctria cinnabari?ia (Tode) Fr., a conmion fungus char- 

 acterized by small cinnamon-colored pustules occurring on 

 dead wood, follows winterkilling, sun scald, etc. It is 

 especially noticeable on winterkilled twigs of Norway 

 maples. 



Oyster mushroom (Pleurotus sapidus Fr.) is a large, 

 edible fungus growing in masses on maples that have been 

 injured by borers and other agencies. A mildew ( Uncinula 

 circinata E. & E.) sometimes infects the leaves of various 

 maples. 



Sun scald and frost cracks are not uncommon on 

 maples. The rock maple is one of the most susceptible 

 trees to sun scorch and "bronzing" of foliage induced by 

 excessive transpiration during dry periods. The red maple 

 is susceptible to winter injury of roots, and like the rock 

 maple suffers from drought. 



Horse-chestnut (Msculus). — Leaf spot (Phyllosticta 

 sphwropsoidea E. & E.) appears in the early summer, and 



later causes a conspicuous yellow spotting of the foliage. This disease is more or 



less common every year. The leaves of the horse-chestnut are occasionally affected 



with mildew (Uncinula flexuosa Pk.), and the 



winterkilled twigs are sometimes attacked by 



Nectria cinnaharina. 



Chestnut (Castanea) . — This is seldom 



planted as a shade tree, although it is some- 

 times seen on country roadsides and on lawns. 



The chestnut blight, which is so serious and so 



universally distributed at the present time, 



renders the use of the species as an ornamental 



tree out of the question. The chestnut is also 



affected with certain leaf spots, etc. 



Sycamore (Platanus). — The tree most likely 



to be severely defoliated by a fungus is the 



sycamore. The causal organism is Glceosporium 



nervisequum (Fckl.) Sacc, which affects the 



petioles and veins of the leaves, causing small 



black areas on these organs. More or less large 



portions of the leaves turn brown and the leaf 



finally falls. 



The sycamore is unusually susceptible to 



winterkilling of the twigs, but in spite of this 



constant defoliation and twig killing it is a very 



hardy tree. 



Poplar (Populus). — The principal species 



in cultivation as shade trees are the Carolina 



poplar, white poplar, Italian poplar and the 



Lombardy poplar. The Italian poplar is often severely affected with rust 



(Melampsora populina (Jacq.) Lev.), and a mildew (Uncinula salicis DC. Wint.) 



is frequently observed on the leaves of poplars. Anthracnose (Marssonia populi 



Fig. 64. — Horse-chestnut leaf spot 

 (Phyllosticta). 



