Trees and Timber 381 



Septoria. Alder, ash, birch, chestnut, dogwood, 



hackberry, maple, oak, pine, poplar, 

 sweetgiim, sycamore, walnut, willow. 



Stigmatea. Juniper, sequoia. 



Taphrina. Alder, birch, elm, hornbeam, horse-chest- 



nut, maple, oak, p. 394, poplar. 



Venturia. Ash, birch, mountain ash, poplar, willow. 



Powdery-mildews. — The general character of these dis- 

 eases and modes of treatment are discussed on p. 122. The re- 

 marks made above regarding leaf-spot apply to the powdery- 

 mildews as well. The chief trees on which they occur are: 

 alder, ash, beech, birch, butternut, catalpa, chestnut, dog- 

 wood, elder, elm, hackberry, hickory, horse-chestnut, honey- 

 locust, linden, locust, maple, mulberry, oak, p. 394, pecan, 

 p. 394, poplar, shadbush, sycamore, walnut, willow. 



Special Hosts 

 ASH 



White-rot "^"^ (Fomes fraxinophilus Peck). — In certain 

 localities in Missouri, Iowa, Oklahoma, Nebraska, and Kan- 

 sas this disease affects 90 per cent of the trees. It prevails in 

 the Mississippi valley and east to the Atlantic. The heart- 

 wood first darkens, and later becomes soft, pulpy, and yel- 

 lowish. The shelving, pored sporophores, 5-10 cm. long 

 and nearly triangular in section, are numerous, chiefly 

 near stubs or wounds, appearing soon after infection. The 

 old, upper surface is brown or black, and very hard. Trees 

 of any age are susceptible, but those over 10 cm. in diameter 

 are most subject to attack. Diseased trees should be cut 

 down, or excision practiced. 



Rust {Puccinia jraxinata (Lk.) Arth.), — This is a rust 

 which may be recognized by the orange-colored cluster-cups 

 upon the swollen parts of the leaves and petioles of nearly 

 all species of ash. The winter condition is found upon 

 marsh-grass, Spartina. Usually the injury is not large, but 

 in seasons favorable to the disease defoliation may result. 



